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October 8

Headset to hear dictations

What are the technical specifications that we have to look in a head phone to get maximum efficiency to hear dictations and comfort for wearing long hours?

As far as comfort goes, that's not likely to be a question of technical specifications. Your head and ears are pretty unique in their shape, and what is comfortable for one person may not be comfortable for you, and vice versa. -- Captain Disdain (talk) 01:17, 8 October 2008 (UTC)

For example, I switched from earmuffs (which I otherwise prefer) to plugs after I got new glasses whose shafts stand out further from my head than before. —Tamfang (talk) 05:34, 8 October 2008 (UTC)

Sensory Integration Disorder and its Impact on Potty Training

I have a 4 yr old daughter who has SID and is very hypersensitive. She has been working with OT and PT since she was 5 mths old. No one has any clear information to give me on how to potty train! The developmental specialist states to give her time- the uroligists states she must get it done b/c of the severe negative side effects it has had on her (kidney infections that have led to hospitalizations). She is very fearful of even sitting on the toilet much less wanting to be in the bathroom when it flushes! I have read all I can find on SID and own numerous books on potty training. Are there methods used for children with SID to help with this issue??

Thank you- —Preceding unsigned comment added by 12.202.108.191 (talk) 03:25, 8 October 2008 (UTC)

Have you asked the medical professionals for locations of appropriate support groups? Have you tried searching on the web for support groups that address this specific issue? There are lots of parents here, but we're really not allowed to give medical advice on specific issues. Franamax (talk) 05:01, 8 October 2008 (UTC)

And there's no particular reason the child must be in the bathroom when the toilet flushes. She can be standing just outside the door watching when you flush the toilet, and then she can hold a long stick to help you flush the toilet, and then she can use the stick herself. But that's starting to be medical advice... Franamax (talk) 05:07, 8 October 2008 (UTC)

Strange gender inequality in the dental industry

I've been to numerous dentists. Why are the dentists always only men and the assistants always only women? Are you ready for IPv6? (talk) 03:49, 8 October 2008 (UTC)

That's an interesting question. Have you tried to seek out dental clinics where the dentists are female? As far as the gender split goes:

• Dentist does seem to be a male-dominated field. A discussion on possible gender-bias can be found here. Stand-alone professional fields such as dentistry would seem good ground for women to avoid gender bias, since they have only to fulfill the qualifications. I would speculate that those women so inclined might gravitate instead to pharmacology or in particular physiology (M.D.-type doctor rather than D.D.S-doctor). Perhaps those women inclined to a medical field either go big or go home (pace to any dentists who might think I denigrate their important field - but it does rank just a little under M.D.).
• As far as dental assistants or dental hygienists, I would speculate that the field offers a good way for women of child-bearing age to acquire a valuable transferable skill that offers them maximum flexibility as to hours worked, balanced with a good income. Also, women are probably just better as dental assistants, since they're more empathetic, interact naturally with children, etc. You can read that as a sexist statement, but I mean it as a statement of great admiration.
• And the factor of bearing and caring for children must always be considered in choice of training and work for women - they're the ones making them after all. :) In the case you question though, the balance does seem somewhat skewed. Franamax (talk) 04:55, 8 October 2008 (UTC)

My current dentist is female, my former dentist was female. Of the 4 dentists over my life-time 2 have been female. Of course that's my perspective and so statistics might not back this up. Just throwing that in there. 194.221.133.226 (talk) 10:32, 8 October 2008 (UTC)

Could it be the case that greater (on average) physical strength and large hands are an advantage when pulling teeth? Or that the general wisdom is such - thus discouraging some women from taking up dentistry? A personal observation - the only time a female dentist tried to remove one of my teeth (I've had a lot of teeth removed), she wasn't strong enough to budge it and had to go fetch a male colleague. --Kurt Shaped Box (talk) 10:59, 8 October 2008 (UTC)

Personal observation #2 - my lower wisdom teeth had twisted roots and the (male) dentist couldn't pull them no-how. He ended up jack-hammering them into pieces (which I still have). As well as the pain from the extraction site, I had a bruise on my jaw from where he braced his hand trying to pull. The point about physical strength may have some merit. Franamax (talk) 21:24, 8 October 2008 (UTC)

This site has some numbers. It says there is an 83%/17% male/female split among all private practice dentists in the US. It's interesting to note that at a prestigious veterinarian school in my area there is a similar split in the other direction. --Sean 14:51, 8 October 2008 (UTC)

It's probably the same reason that most Doctors (traditionally) have been male, and most Nurses female. "Dentist is to Doctor as Dental hygienist is to Nurse" (FWIW, my current dentist is female, and I know of male hygienists, just like I know female doctors and male nurses) -- 128.104.112.147 (talk) 15:40, 8 October 2008 (UTC)

A dental hygienist is different from a dental nurse. --Tango (talk) 23:23, 8 October 2008 (UTC)

I'm a male and I don't work out very well and probably every woman in the miitary is stronger than me so I don't think it's strength. As for pregnancy, dentists often share a practice with another dentist and dentists themselves generally see the patient for two minutes during checkup. I also have noticed there's a lot of female vets. I'm not really quite sure how to really search for lots of dentists. I usually call 800-DENTIST when I move, but my last move within about 50 miles only one dentist was registered. That dentist had a nice office with fancy machines so I thought he'd be good. It turns out that he pays for it all by not just charging 4 times more for an exam, but will give false diagnosis and tell people they need expensive things done that only harm their teeth. I wasn't certain until I searched on the internet about this. There's countless cases of people who moved to a new location, got a new dentist, and despite having no cavities or other problems for 10-15+ years their new dentist claims to find 5-12 cavities that don't exist just so he can mutilate a person's body to make extra money. It's rather common. I take it dentists don't have to take the hipocratic oath. Are you ready for IPv6? (talk) 01:39, 9 October 2008 (UTC)

Well, if you just wanted to rant about how evil dentists are, you could have saved us some time and effort answering what looked like a legitimate question. How's this then? Dentists are a male-dominated caste placed on this earth solely to suck away our cash and destroy our bodies. There you go, you read it here on Wikipedia, so it must be true. Can we close this thread now? Franamax (talk) 02:51, 9 October 2008 (UTC)

That wasn't reason for the question. I just bought it up along with a lot of othe things because I saw a lot of people discussing this. Are you ready for IPv6? (talk) 03:41, 9 October 2008 (UTC)

OK, I'll retract any suggestion that you posed an improper question in the first place. However, the later post you made strays over the line into our striction that the RefDesk is not a forum for opinions, nor is it a soapbox to put forth your own opinions. If you have a specific follow-up question, we can consider it. Franamax (talk) 03:47, 9 October 2008 (UTC)

It seems that over-servicing is not an article here though Google attests dentistry is rife with it. Dentistry may not have the hippocratic oath as such, but its national professional association would have an ethical code and is the body to complain to usually. On wiki, entering "Dental ethics" gives you Michele Aerden who instigated the first Dental Ethics Manual and "Dentistry ethics" comes up with stuff worth sifting if you're keen. Julia Rossi (talk) 10:45, 12 October 2008 (UTC)

immume system

types of immumoglobine —Preceding unsigned comment added by Ksneyhaa (talk • contribs) 06:37, 8 October 2008 (UTC)

WIth regard to the immune system, we discuss immunoglobulins IgA, IgD, IgE, IgG, and IgM. - Nunh-huh 06:43, 8 October 2008 (UTC)

chemistry

two flasks A & B have equal volumes .flask A contains Hydrogen maintained at 300K while B contains methane gas maintained at 600K. 1.which flask contain greater number of molecules & hwmany times more —Preceding unsigned comment added by Bhuwanntl (talk • contribs) 07:55, 8 October 2008 (UTC)

"Do your own homework. The reference desk will not give you answers for your homework, although we will try to help you out if there is a specific part of your homework you do not understand. Make an effort to show that you have tried solving it first." -- Aeluwas (talk) 08:53, 8 October 2008 (UTC)

Your question is unanswerable, because you have not specified whether the two flasks have equal pressures. Take a look at combined gas laws. If we specify that pressure is equal, you're looking at Charles's law. - Nunh-huh 09:00, 8 October 2008 (UTC)

Aflatoxin in raw peeled peanuts

How can I know if raw peeled peanuts are contaminated by Aspergillus flavus and Aspergillus parasiticus? Is it possible to see it like mold on bread? Mr.K. (talk) 12:14, 8 October 2008 (UTC)

Peanuts in general are susceptible to aflatoxin contamination. You wouldn't see the aflatoxin itself (except under blacklight), but you might see the fungus that produces it. Cooking doesn't really affect it, since the toxins are heat stable (the fungus that produces them, however, is not). Fungus doesn't imply aflatoxin (not all fungi produce it), but lack of fungus doesn't guarantee safety. Like most toxins, a really small dose (i.e. one dubious peanut eaten per year) isn't going to kill you. If in doubt, don't eat it (no surprise there), but probably best to avoid the whole group if you see some fungus growing on anything in it. SDY (talk) 13:01, 8 October 2008 (UTC)

Sleep injuries

I'm failing to find the medical term for injuries that occur while sleeping, such as pulling a muscle or separating a joint. Is there a term to classify those injuries? -- kainaw™ 13:18, 8 October 2008 (UTC)

They don't happen often enough, and aren't intrinsically different from similar injuries occurring while awake, for there to be a common medical name for them. - Nunh-huh 15:22, 8 October 2008 (UTC)

Semen and Enzymes

Do the enzymes in washing detergent break down the proteins ect, that are in semen? i always wash my underwear seperately, because i worry that im simply spreading it all evenly on my clothes, and that microscopic amounts will rub off on where i sit ect. Zakbrak341 (talk) 13:56, 8 October 2008 (UTC)

If they're only microscopic amounts, what difference does it make? Also, why do you have so much semen in your underwear? You're meant to remove your clothes for that kind of thing... --Tango (talk) 14:10, 8 October 2008 (UTC)

Its not loads, just very small amounts of precum before i take them off ect, if got lots on them i'd just throw them away, but the thought of any amount of semen on anything bothers me, for a while i was doing a hot wash, so it would denature the protiens but then i worried that the heat would denature the enzymes in the powder, and if the enzymes break down the protiens into amino acids, then thats better than simply unfolding the protien into its secondary of primary structure, then i started worrying, what if these enzymes in the washing powder are specfic to protiens in common food stains only and have no effect on the protiens in semen, so now im just wash them in serveral changes on water with lots of detergent. —Preceding unsigned comment added by Zakbrak341 (talk • contribs) 14:31, 8 October 2008 (UTC)

Tango, two things. First, some people are kinda clean freaks when it comes to everything, so it's not really unusual to be concerned over whether semen is contaminating other clothes in the washing machine. Secondly, it's not really your place to ask him why he has semen in his underwear, you should only address his questions. 98.221.85.188 (talk) 14:35, 8 October 2008 (UTC)

Your detergent should emulsify fats, which means that it wraps little bubbles of detergent around your semen and stops it from sticking to any of your clothes. Plasticup ^T/C 15:08, 8 October 2008 (UTC)

Except that semen is essentially fat-free. No emulsification. For the original questioner: the enzymes in washing detergents are designed to be as non-specific as possible in breaking down proteins, and should have no trouble with semen. - Nunh-huh 15:19, 8 October 2008 (UTC)

Even if someone can get something which is soiled physically clean, meaning that the offending sunstance cannot be seen or even detected by CSI, they still remember it was once there. It can get more into ritual purification, like the concept of a ritual bath removing some iniquity or moral stain. I read a housewife's complaint to an advice column that her husband had soaked his sore toe in warm salt water (at the doctor's advice) in one of her expensive gourmet cooking pots, and that she had to throw the pot away because she would never afterward feel that it was "clean" regardless of scrubbing or dishwasher cleansing. If the questioner gets a reference to an authoritative laundering site which says a wash of some temperature on some cycle with certain cleaning products will render the garment as clean as it was when it came out of the package, then he might be saved the expense of frequently throwing garments away and buying replacements. Some people, even in this era of "cold water" energy-saving detergents wash a load of white cotton washcloths, towels, and underwear in the "hot" wash cycle with detergent and chlorine bleach, with an extra rinse, Not saying this is the authoritative answer to the original question, and there is also the question of enzymes versus bleach and hot versus cold water to eliminate biological stains. Interestingly there are loads of book references dealing with semen stains[[1]] though few specifically address their removal. (Not to be confused with the mythical character "Seaman Staines" on the Captain Pugwash children's program). Edison (talk) 15:23, 8 October 2008 (UTC)

You can check how good a job your selected detergent is doing by taking a look at your unmentionables under a black light before and after the wash. 71.178.135.144 (talk) 02:15, 9 October 2008 (UTC)

Not a great method. While semen does fluroesce under a black light, it is not the only thing that does. Lots of detergents and fabric softeners do, as well. When you see, on crime shows, them use a black light to look for semen and/or blood, it's not the black light that proves its presence; the black light merely lets them know where the most likely places to test are. Its only after they have done a positive chemical test can they know that the stain that glows under black light is semen, or blood, or any of a number of other agents that also glow... --Jayron32.talk.contribs 02:24, 9 October 2008 (UTC)

If it makes the questioner feel any better, the sperm in semen dies after the semen dries, so no matter what, there is no sperm spreading around your clothes or to any other surfaces.--el Aprel (^facta-_facienda) 20:20, 11 October 2008 (UTC)

E=mc^2...Whatever that means.

Hey...what unit is the E in $E=mc^{2}$? Is it calories, Joules, tons, or what? I have been wondering about this for a while and saw the article on E=mc^2 with its handy list of how much energy is contained in a dollar bill. It lists several units of measuring energy, which got me confused. When you convert mass to energy, is the mass converted to Joules or calories or another type of energy? 31306D696E6E69636B6D (talk) 16:36, 8 October 2008 (UTC)

Well, it defaults to kg·m²/s² (Joules), which it does say in the intro :)

In the formula, c2 is the conversion factor required to convert from units of mass to units of energy. The formula does not depend on a specific system of units. In the International System of Units, the unit for energy is the joule, for mass the kilogram, and for speed meters per second. Note that 1 joule equals 1 . In unit-specific terms, E (in joules) = m (in kilograms) multiplied by (299,792,458 m/s)2.

-- MacAddct1984 ^{(talk • contribs)} 16:42, 8 October 2008 (UTC)

(ec) :Joules and calories are units of measurement, not different "type[s] of energy". Just like you can measure speed as miles per hour or kilometers per hour or feet per second and can convert a speed from one to the other but it's still the "same speed". So whatever units you use for c and for m determines the units of E. If that's not the unit you want, you can convert. Or you can choose what units of energy you want and then convert the mass and speed of light to use them. DMacks (talk) 16:43, 8 October 2008 (UTC)

As long as you're consistent, you can use any unit system (for example, you could use ergs, but then you would have to measure the mass in grams and the speed of light in cm/s - see cgs). Usually scientists use SI units, where energy is measured in joules. It's also common to see energy measured in electron volts. --Tango (talk) 16:46, 8 October 2008 (UTC)

You're wrong: you can use any units that measure the same thing. For example, instead of asking how many 'joules' a certain number of 'kilograms' would result in according to e=mc^2, you can ask Google how many "horsepower-hours" (which measures the same thing joules do) a "pound" of stuff results in. Just google "1 pound * c^2 in horsepower*hours". You get "1 pound * (c^2) = 1.51859015 × 1010 horsepower * hours". In other words, if you had a magic reactor in your room that completely turned matter into energy, then with 1 pound of fuel you could output one horsepower (745 watts) for

15000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 hours.

You haven't used the same equation, though, you've added a conversion factor (or, you've absorbed the conversion factor into the constant by measuring the speed of light in obscure units). You have to use consistent units, otherwise you quite clearly get nonsense. If I use kg for the mass and m/s for the speed, plug it in and I get joules for the energy, I can't just choose for that to be ergs or electron volts or horsepower hours, since that would be assuming they are all the same thing. To get to another unit I had to multiply by a conversion factor so then I'm actually using E=kmc² where k conversion factor. --Tango (talk) 21:12, 8 October 2008 (UTC)

No, you're just wrong. Take something simple: distance = speed * time. So, 60 miles per hour for two minutes = distance = 60 m/h * 2 minute = 120 minutes * m/h, ie "120 mile-per-hour minutes". And look 120 mile per hour * minutes = 3.218688 kilometers is a perfectly good answer. You can ask for it in feet, inches, anything. It's just a unit conversion, it's not solving an equation. —Preceding unsigned comment added by 82.120.232.170 (talk) 12:26, 11 October 2008 (UTC)

yeah, just remember that the CONSTANT in the equation, C, isn't just a number, like a million. Instead, it's a "million miles per hour" (for example). So, if you take a pound, or a kilogram, or any unit of mass you want, and mulitply it by a million miles per hour squared, you get a certain amount of energy. I don't have an intuitive conception for why a million miles per hour squared times 1 pound should be an amount of energy though... —Preceding unsigned comment added by 82.120.232.170 (talk) 17:54, 8 October 2008 (UTC)

Lets take it in terms of the metric system, for symplicity. Energy is defined, in one instance, as the measure of the change of speed of object of a defined mass over a defined distance. From a unit-based analysis, that means that energy is measured as kilograms times meters squared divided by seconds squared, ( kg*m²/s² ). That is the inherent definition of energy. The deal is, if you do ANY other combination of measurements, and arrive at the same final units, that is a measure of energy. For example, air pressure*volume is a unit of energy (air pressure can be expressed as force per unit area, and force is mass * acceleration, and volume is displacement cubed, so the if we express pressure as (kg) * (m/s²) / (m²) * (m³) we get, kg*m²/s², which is energy. How we calculate energy, as electron-volts or as newton-meters, or as joules, or as liter-atmosphere (these are all energy measurments) is largely dependent on the particlar application. --Jayron32.talk.contribs 18:18, 8 October 2008 (UTC)

I've thought of an analogy that might help you: if you could increase your gas mileage by 20% for every 10% under the speed limit that you go (just made that up!!!) you can use that without knowing units for EITHER mileage OR speed limit -- and indeed, our British readers would translate that "tip" into different actual numbers than the Americans...

So if m is kilograms then E would have to be in Joules? 31306D696E6E69636B6D (talk) 18:29, 8 October 2008 (UTC)

No, you're confused by the mistake the poster above made. See my correction of him above. (The poster above is lazy and wants to just cross out units that are the same, for example, when you multiply 55 miles per hour by 2 hours you figure out what units the answer will be by going: [m/h]*[h], ie crossing out the two h's. But you can just as easily ask what distance you go in a minute at that speed).

The easiest thing to do is play around. Into google put "c=" . Then try "1 lb * c^2". And put "1 kilo * c^2". Then you can ask for the results in different units by saying "in" as I did above ("1 pound * c^2 in horsepower*hours").

If m is in kg and c is in m/s, the E will be in joules. If you chose different units for c, you'll get different units for E. --Tango (talk) 21:14, 8 October 2008 (UTC)

Energy is dimensionally equivalent to Force*Distance, which is equivalent to Mass*Speed*Speed. (See Dimensional analysis for a better grounding on the subject.) The exact units that Energy comes out in is dependent on the units that you use both for mass and for speed. $E=mc^{2}$ is always valid, regardless of choice of units for any two of the quantities, however, the units of the third may end up not to be a "conventional" measure (e.g. $stone*furlong^{2}/fortnight^{2}$ is a unit of energy, albeit not one that has much use/respect). SI, however, is designed to be self-consistent, so if you stick to the standard SI units, things tend to work out well, unit-wise. Kilograms, meters, and seconds are all base SI units, so for mass in kg, and speed in m/s, the units of energy work out to the SI unit of energy (joule), because the joule is defined as equal to $1kg*m^{2}/s^{2}$ (See joule#Description). -- 128.104.112.147 (talk) 22:27, 8 October 2008 (UTC)

I think a workingman's explanation of e=mc^2 is prudent here. When you convert mass to energy, you are literally doing just that. Mass becomes energy. The 'type' of energy mass becomes is actually explicit in the formula. When mass is converted to energy, for instance in a nuclear reaction, it is released as a photon, which is why we use 'c' as a conversion factor: the mass is converted into light! --Shaggorama (talk) 07:46, 13 October 2008 (UTC)

Except that E=mc² holds for all mass-energy conversions, not just the ones which involve photons. For example, with beta decay, the weak interaction causes a neutron to decay into a proton, an electron, and a neutrino - no photon involved. Yet, there is a detectable reduction in the total mass of the system, which correlates to the amount of energy released by the decay by the equation E=mc². It gets even stranger. The mass of a proton is about 60-160 times that of the three quarks of which it is composed (the gluons being massless). Where does the extra mass come from? It's mainly the binding energy of the three quarks, along with the kinetic energy of their relative motion. Absolutely no photons involved, yet this mass-energy equivalence is still governed by E=mc². The use of c is due to its property of being a fundamental metric of 4-dimensional spacetime (specifically, the conversion factor which allows you to interconvert time with spacial distance) - the fact that it is also "the speed of light" is just a side product of that, not the key essence of the quantity. -- 128.104.112.147 (talk) 23:20, 13 October 2008 (UTC)

safe dough?

I live with an Italian, and she's making pizza in four days -- but she's started today. She mixed a spoonful of honey with oil into flour and water and is letting it rise at room temperature, keeping it moist under a moist cloth (which she will keep remoistening over the next four days). This "mother" dough she will use over the course of several pizzas, the first one Saturday, until she's done with it.

My question is: how does this work? I'm not sure what role the "mother" dough has, is it like yeast?

In fact I heard that "sourdough" was created by accident more than a hundred years ago, and since then they have alwyas been reusing the same starter -- they always saved a little to make more. But she's not adding a "starting" piece, she's just starting from honey and oil! So, isn't it just a random toss-up what microbes will start growing? Why is it even safe?

Obviously I'm not asking for any medical or legal advice... —Preceding unsigned comment added by 82.120.232.170 (talk) 17:14, 8 October 2008 (UTC)

Actually, the invention of having isolated yeast which you add to the dough to make it rise is a relatively recent invention. For thousands of years, bread was made the same way: You mixed flour, water, and a few seasonings, you sat the mixture on the window sill, and it picked up whatever yeast cultures blew in on the wind, and the bread rose and you baked that. The problem is that some cultures don't taste particularly good. Someone a long time ago figured out that if you find a particularly tasty piece of dough, rather than let future batches of dough get cultured randomly, if you innoculate it with your good-tasting culture, you get equally good tasting bread. This is often accomplished by reserving a "starter" or "mother" culture from each batch of bread, and using it to innoculate the next batch. However, you can also control which cultures take hold in your bread by carefully controling the chemistry of the dough. Cultures are highly sensitive to variations in pH and salinity and other factors, so the specific ratios of say, honey to salt to flour will basically be highly favorable to a single variety of microorganism, and not so much to the others. Once you find a recipe that attracts the right yeast, if you use the same recipe each time, you will end up with the same yeast each time, and thus a fairly consistent bread. --Jayron32.talk.contribs 18:04, 8 October 2008 (UTC)

(EC) See sourdough, which is exactly what she's making; it should be delicious! The reason it's not a toss-up is that whatever incidental microbes might be hanging around get their asses kicked by the massive amounts of good yeast and bacteria already in the flour. It's only if they run out of food (the honey) that those agents will start to die off and bad ones can take over. Sourdough has been around for thousands of years, and while it is indeed possible to keep a starter going indefinitely, most people just start one from scratch. --Sean 18:15, 8 October 2008 (UTC)

if I get you right, your response implies 1) flour you buy has lots of good yeast and bacteria in it (and not bad ones), it's made that way? How's that work? 2) if you added honey forever the good ones would always have enough to eat, you could keep it going a month and then bake it... —Preceding unsigned comment added by 82.120.232.170 (talk) 19:45, 8 October 2008 (UTC)

Actually, most of the yeast is present in the air, or on the flour itself. The yeast is just there, it isn't added or anything. It may grow on the grain naturally, or it may just alight on the flour from the air. The determining factor as to which microbe predominates is the local chemistry in the dough. The good yeast, if correctly encouraged to grow, will simply crowd out any nasty critters. --Jayron32.talk.contribs 20:09, 8 October 2008 (UTC)

In fact, the use of "ambient" yeast and bacteria in lambic beer rather than pure yeast cultures is the reason for the rich complex taste of Belgian beer. - Nunh-huh 21:03, 8 October 2008 (UTC)

1) Correct. It's only natural that microbes that can live on wheat will be found on it in the wild. 2) No, just adding honey won't do it. You also need to add more flour, and water, and keep the bacteria/yeast balance correct. I seem to remember Harold McGee's magisterial On Food and Cooking covering the details, but I'm sure many baking books do, too. FYI, some cooks have kept starters going for *decades*, though refrigeration makes that a lot easier. --Sean 22:32, 8 October 2008 (UTC)

We cannot rule out that "wild" yeast or fungus might make the dough taste bad or even become toxic. Edison (talk) 03:53, 9 October 2008 (UTC)

An archived Ref Desk answer describes some undesirables which might grow in a dough culture : "I suppose we could add a disclaimer about "Ask a baker" or "Ask a mycologist" for bread mold advice. I claim no expertise in this area and only cite info found on the net or from general reading, including a baking textbook, and from baking various types of bread in the home. The surface of fresh-baked bread is generally free of microorganisms because of the heat of baking, but ropy mold may survive in the interior of bread. The surface can become contaminated while the bread is cooling or being wrapped, while it is sliced, or while it is stored. [2]. Bread can be attacked by various types of mold. There are over 600 varieties of bread mold. Some of them are listed at [3]. Note that the same mold may grow on bread and other substances, and some of these are toxic to humans. In general, some spores are just part of nature. But if mold from bread or other sources has left a high concentration of spores in an area such as your kitchen or your breadbox, it stands to reason that a loaf of bread placed there subsequently might get moldy quicker than if the mold spores were not drifting around. See Black bread mold, [4] at Madsci.org. Edison 14:59, 14 August 2007 (UTC)" Edison (talk) 18:49, 9 October 2008 (UTC)

and, of course, once you've made a few loaves of bread in a kitchen it's pretty thoroughly inoculated with enough yeast on a permanent basis. fungi are remarkably tenacious. I worked in a lab with the fungus neurospora crassa 20 years ago; i'm still seeing random colonies of neurospora appear around the house where i haven't hit it with the lysol lately, along with the usual household mildew and random gunk. mind you, i didn't grow the fungus at home, that's just from spores which hitched home with me; and moreover, I've moved twice since then. for another example, microbreweries which make beer for on premises consumption but subcontract the bottled product to big breweries (often the case) can specify their recipe, but can't specify their particular strain of yeast, as one particular strain of yeast will colonize a brewery, and you just can't make a batch with a different strain in that premises. (so i've been told at the local microbrewery). see also lambic for another example of trusting in airborne yeast to produce a palatable and nontoxic product, rather than adding a defined yeast (oh, somebody said that already). Gzuckier (talk) 06:03, 11 October 2008 (UTC)

Erronious definition

I found this definition for Hyperthyroidism. I don't believe this is the real definition. I couldn't figure out how to correct it so I am sending it to you.

<obvious bit of vandalism removed ... no need to keep that around for posterity --98.217.8.46 (talk) 03:13, 9 October 2008 (UTC)> —Preceding unsigned comment added by 152.130.7.64 (talk) 18:27, 8 October 2008 (UTC)

Yes, that's a bit of vandalism in our hyperthyroidism article. It's fixed now, thanks for pointing it out. - Nunh-huh 19:09, 8 October 2008 (UTC)

Perhaps it's an alternate definition? --Sean 22:38, 8 October 2008 (UTC)

Perhaps in an alternative universe. - Nunh-huh 23:32, 8 October 2008 (UTC)

Do gas giant even have a flowing water?

Do Jupiter, Saturn, Uranus, and Neptune even have a flowing water in it's mantle or it's just a hot dense white-hot vapor if human touch it they will instantly get electricute and roast. All their core is very white-hot, hotter than the surface of the sun.--SCFReeways 23:13, 8 October 2008 (UTC)

To be honest, I'm not sure. Any water in the mantle would be extremely hot, but the pressure may be enough for it to stay liquid. I think it would be all mixed in with everything else rather than flowing, though. A human at those temperatures would be instantly killed, yes, although I don't know why you think they would be electrocuted... --Tango (talk) 23:20, 8 October 2008 (UTC)

• metallic hydrogen for jupiter and Saturn, certainly they conduct electricity, even Uranus and Neptune the ice to me actually means electronic stuff, hot gluey vapours similar to lightning and molten comets. I don't think is true water the water we use and drink. Those planets is total gas, and landing to me is like going to hell. No solid surface no place to land, from what I've learnt when I was elementary student, if we try to land on it we will just keep sinking trough their interior, until we get to it's nucleus, and even prior to getting to it's center, the strong heat will instantly kill humans, even those dense vapours. Does your saying of liquid mean vapours from the burnt rockets?--SCFReeways 23:36, 8 October 2008 (UTC)

To answer Tango's question, I presume the OP is concerned about that big-ass storm that's been circling Jupiter for at least the last 300 years. And there's plenty of lightning on Jupiter (at least) and presumably the other gas giants. Matt Deres (talk) 23:42, 8 October 2008 (UTC)

• Even Uranus and Neptune's mantle I beleive is made of deadly "junks" possibly liquid, eelctrical wastes, vapors, perhaps anything.--SCFReeways 23:51, 8 October 2008 (UTC)

I think we can all agree that anyone standing in the core of a gas giant would be killed instantly. The heat and pressure would be extraordinarily deadly. I'm pretty sure you would not live long enough to be electrocuted by a lightning bolt.

Does that answer your question? APL (talk) 01:35, 9 October 2008 (UTC)

Heat, pressure AND radiation. The gas giants are certainly pretty nasty places. Given that there must be a more or less continuous gradient from the low temperature and pressure of space down to the metallic hydrogen at the center - you'd imagine that there would be some altitude at which liquid water could exist - whether there actually is enough water at that level to form flows is much harder to determine. Probing the conditions deep into that atmosphere is very hard. SteveBaker (talk) 01:53, 9 October 2008 (UTC)

Are you saying gas giants have a core that is just gas? Not rock? I'd assume enough asteroids fell into them to give them a rocky core, though I hear Saturn is very light. Though I also would assume then that the sun must swallow a lot of asteroids, though why this doesn't make the sun die with iron going into its core, who knows. Are you ready for IPv6? (talk) 03:39, 9 October 2008 (UTC)

Talking about Earth or gas giant? While Earth have "Greenhouse" or "Icehouse" have nothing to do with gas giants. Earth had icehouse in the past, and once it was cooler when all the continenets is at the South Pole. 100 to 200 million years later, Earth will likely to be greenhouse or hot again. I don't know why you ask this becasue this have nothing to do with the question.--Freeway91 19:58, 9 October 2008 (UTC)

Gas giants have a solid core, but not because they swallow asteroids, it's because of the immense pressure. 98.221.85.188 (talk) 04:17, 9 October 2008 (UTC)

I don't think the core is rock as we know it. In Jupiter's case, at least, it's rather exotic matter (metallic hydrogen and similar), due to the intense pressure. Regular rock would probably be destroyed long before it reached the core. --Tango (talk) 10:23, 9 October 2008 (UTC)

Well, the elements that make up the rock (iron, etc) have to be there somewhere. In these cases, though, it's a matter of scale. Neither Jupiter nor the Sun consume enough asteroids to be relevant when analyzing their overall composition. — Lomn 13:01, 9 October 2008 (UTC)

Sure, the elements will be there, but not in the forms we're used to. They had plenty of the components of rock from the start, they don't need asteroids for that (well, they make have formed by aggregation of what were essentially asteroids, but that was a long time ago), but those components can't make rock at those temperatures and pressures. --Tango (talk) 13:36, 9 October 2008 (UTC)

I wonder if consumered rock has anything to do with the sun cycles like the sun is supposed to go in cycles where it varies from stronger and weaker to what it puts out. I know that the earth while it did go into cycles of hot to freezing, did used t average a lot hotter but in the last tens of millions of years it gradually really cooled down and then the recent ice age was pretty much its lowest point and then it started warming back up a bit, but still lower than the average. Mars was also supposedly warmer at one time, too. Are you ready for IPv6? (talk) 13:46, 9 October 2008 (UTC)

Highly unlikely, again as a matter of scale. There's just not enough foreign material entering the sun to affect things, even if things would be affected in the first place. With that caveat, it's worth noting that even dropping a planet-sized chunk of iron into the sun would likely have no effect. Iron is the fusion stage at which stars quit, yes -- but the presence of iron should have no effect on the hydrogen fusion process currently ongoing, or the helium fusion that will follow once the hydrogen is exhausted, or the lithium or beryllium or whatever follows that. Iron isn't exothermically fusible, but neither does it poison other fusion reactions. — Lomn 14:08, 9 October 2008 (UTC)

Metallicity does affect how a star behaves, but I agree that on the scale we're talking about the effect would be negligible. I'm not sure much even falls into the sun - to do so it would need to shed almost all its angular momentum, which is pretty difficult to do. --Tango (talk) 14:18, 9 October 2008 (UTC)

Time-independent Schrödinger equation: "If $\psi$ is a solution then $\psi$* is also a solution."

In an Introductory Quantum Mechanics book I'm reading, the author often claims that if $\psi$ is a solution then so is its conjugate, and this is stated as being self-evident (leaving me to suspect I'm missing something obvious). Previously, I've only ever encountered complex conjugates when related to an actual complex number, whereas $\psi$ is actually a function $\psi (x)$, hence my confusion.

The equation is as follows:

$E\psi =-{\frac {\hbar ^{2}}{2m}}{d^{2}\psi \over dx^{2}}+V(x)\psi \,$

This forms part of a question that asks to show that a time-independent wave function $\psi (x)$ can always be taken to be real, because if a solution isn't real it can just be expressed as a linear combination. Quote: "if $\psi (x)$ satisfies [the above equation], for a given E, so too does its complex conjugate, and hence also the real linear combinations $(\psi +\psi *)$ and $i(\psi -\psi *)$."

So I basically have two questions: 1) Why can we say $\psi *$ is a solution because $\psi$ is? 2) What else is this question looking for, since it basically gives the answer away when it talks about the linear combinations?

I have the feeling I'm mis-interpreting something here, so I'd be grateful for any clarification or help. Leucippus89 (talk) 23:54, 8 October 2008 (UTC)

Edit: Just to be clear, this question is about $\psi (x)$ and not $\Psi (x,t)$. I know that when you solve the Schrödinger equation by separation of variables, the time-dependent function always has complex components which are dependent on t and so could be safely ignored (?) in an equation that's just concerned with x. But that's not what this question's about, and I think that's what's confused me, because I'm not used to seeing complex terms in $\psi (x)$. Leucippus89 (talk) 00:39, 9 October 2008 (UTC)

I suppose $E$, $V$ and $m$ are all real? If so, it's pretty easy to see that $E\psi ^{*}=(E\psi )^{*}$ and $-{\frac {\hbar ^{2}}{2m}}{d^{2}\psi ^{*} \over dx^{2}}+V(x)\psi ^{*}=\left(-{\frac {\hbar ^{2}}{2m}}{d^{2}\psi \over dx^{2}}+V(x)\psi \right)^{*}$. —Ilmari Karonen (talk) 02:45, 9 October 2008 (UTC)

October 9

Sending Sound Wave or Voice Messages to the Past?

Is it possible to send sound waves or voice messages to the past? For example, sending sound through time where the sound could be picked up by a local telephone. Can we build a technology to do this? 72.136.111.205 (talk) 00:19, 9 October 2008 (UTC)

No. --98.217.8.46 (talk) 00:29, 9 October 2008 (UTC)

Currently, humans have absolutely no ability to send anything through time. It's possible we never will.CalamusFortis 01:17, 9 October 2008 (UTC)

Backwards through time...no. Forwards...yes. Relativity allows 'fast-forwarding' of time. From everything we know about the nature of time, there is absolutely no way to send anything back in time. SteveBaker (talk) 01:47, 9 October 2008 (UTC)

If Extrasensory perception worked, you might send the voice message by "mental telepathy" to someone in the past who had the right "gift," by some means beyond the knowledge of present science. Sending a sound vibration to an eardrum or making a voice frequency currents flow in phone wires or sending a telegraph message or affecting a computer circuit would require a transfer of energy, which would seem to violate the conservation of mass and energy in the universe both at the present and in the past. Jumping into the realm of science fiction, I suppose a way around this would be if the person 100 years ago left a message that he would send a message to the future, amounting to a certain amount of energy, and you sent a message with an identical amount of energy to the past, and somehow the messages cancelled, conserving mass and energy. That notion would work for letters or for time travellers of equal mass. Of course, any influence from the present to the past would alter the course of events, meaning that things might proceed a little differently in that time space continuum than turned out in ours. Edison (talk) 03:51, 9 October 2008 (UTC)

The whole idea of time travel is logically inconsistant anyways. If someone could travel in time as freely as in space, it would presuppose some "meta-time" that itself behaved exactly like real time is supposed to behave, but doesn't cuz you are traveling through it. There's a database of causality, and if it isn't time, its something that behaves exactly like it... --Jayron32.talk.contribs 04:13, 9 October 2008 (UTC)

There can be an almost infinite number of parallel universes, with every possible outcome of each quantum choice-point oiccurring, so there is no problem of causality. If I send a message to Kennedy to duck when Oswald shoots, then only that time-space continuum has a second Kennedy term as president, and ours is not affected. If the bread falls jelly side up in one continuum, it falls jelly side down in another. I doubt time travel being possible, because to the best of my knowledge, no chrononaut from the future has ever held a press conference. Edison (talk) 05:42, 9 October 2008 (UTC)

Well, never had a reliable press conference. (There have been claimed chrononauts, e.g. John Titor). --98.217.8.46 (talk) 11:30, 9 October 2008 (UTC)

(undent) Well, WRT the parallel universe problem, that still presupposes a "branching" causality, which can still only be traced in a forward direction. That forward moving coordinate is still behaving exactly like time. --Jayron32.talk.contribs 18:10, 9 October 2008 (UTC)

I suppose that in branching causality, a choice point would be whether or not the chrononaut arrived at a certain time and place. Edison (talk) 18:46, 9 October 2008 (UTC)

There is a problem with the branching 'many worlds' hypothesis for time travellers (I've been thinking a lot about this recently because I've been geeking-out on the latest Neil Stephenson book "Anathem"). So let's review what is generally said about this:

The theory says that in every possible instant in which a quantum event happens (Schrodinger's cat either dies or doesn't die - to pick a typical example), then the universe splits into two copies that are identical in every way except for that one event. So now there are two universes - one with a live cat in the box and another with a dead one. OK - so now, the "future-you" builds a time machine - goes back in time and yanks the cat out of the box when nobody is looking 10 minutes BEFORE the experiment is started. The idea is that your arrival into the past caused another fork in the universe back before the cat did or did not die - so now there is a third path...that the cat was never in the box in the first place. The future-you who jumped back in time didn't come from the "cat not in the box at all" future - but from...oh - but wait...from BOTH the cat-is-dead and cat-isn't-dead universes? Since those two universes are identical in all other respects - it's pretty reasonable to assume that both of you make identical time machines and jump back to an identical past...at a time when there were VASTLY fewer copies of the universe. Since an insanely large number of quantum events have happened throughout the universe between the cat experiment and the time machine being turned on - there are an insanely large number of time travellers all jumping back to the exact same copy of the universe at (typically) the exact same point in space and time. Only very few potential time travellers would fail to make it back because (through random quantum effects) were too grief-stricken by the pointless death of the kitty - or were just ABOUT to turn on their time machines when a cat leaps onto it and destroys it just seconds before launch.

But the fact remains that an almost infinite number of universes have been 'forked' from what was a single universe in the past at the moment in time to which the time machine is aimed. Hence a nearly infinite number of almost identical time travellers would pop into existance at more or less the same instant!

This is a big problem for the 'branching' many worlds concept. The reason I mentioned Anathem is because Stephenson has proposed in it an alternative means for the 'many worlds' thing to happen. I haven't finished thinking my way through the implications of it yet (and all the heavy thinking it requires is slowing my reading of the book to a crawl!) - but essentially he envisages an infinite number of universes proceeding down every possible path through "configuration space" - requiring them to converge as well as diverge! So two universes that have differed only in some very subtle manner could 'collide' and become one universe in which those past differences have quite utterly ceased to matter. This eliminates my complaint rather neatly. But it's not (I think) quite what most many-world-theorists had in mind.

SteveBaker (talk) 04:37, 10 October 2008 (UTC)

So...In Stephenson's book (which, we must emphasise, is fiction) - he proposes that we look at the multiverse in "configuration space". Imagine plotting a graph of (say) the cost of gasoline versus (say) the number of sunspots visibile on the sun...two totally unrelated things. Each point on your graph paper represents one possible combination of price and sunspot count - and if you plot these two things over time - you get a curve that traces around in some bizarre shape - looping back on itself, etc. Well, if you didn't limit yourself to 2D graph paper - you could plot more properties of more things - on 3D graph paper, you could plot price of gas against sunspots against the Dow Jones index. With 4D graph paper, you could add the popularity of the current US president...and if you had a truly INSANE number of dimensions for your hypothetical graph "paper" - you could plot the position, mass, spin, momentum, etc for every single fundamental particle in the entire universe. Since every possible configuration of the universe would be represented by a point somewhere in our bazillion-dimensional graph paper, we can draw a line on that graph that represents the progress of our universe through time...one of Stephensons' characters calls this a "Narrative". We could also plot the narratives of other possible universes through configuration space. OK - so that's Stephenson's idea of configuration space.

When you look at a classical (non-quantum) view of the universe - in which every event is entirely deterministic - the Narrative for our universe would be a L-O-N-G wiggly line snaking it's way through configuration space - looping around a region that's somewhat compact on the bazillion-dimensional graph because so much of the universe is relatively stable. But in a quantum universe like ours where events that are truly random happen and weird superposition phenomena exist - that line branches...just as in the many-worlds interpretation of quantum theory. But viewed in configuration space, it's also possible for two of these Narrative branches to merge back together - if two versions of the universe that differ only by the location of one fundamental particle happen to arrive at the same point in configuration space because that particle ended up in the same place in both of them - making the two universes identical in every respect. This is rather nicer than the conventional "many worlds" picture where universe split into copies of themselves - but never come back together again.

So what we have in Stephenson's rather clever model is that every conceivable point in configuration space (even some crazy, impossible-seeming ones) "exist" in some sense - and each one changes over time by threading a line through that bazillion-dimensional graph - sometimes splitting into two because of quantum randomness - other times merging together because two universes that have (potentially) very different origins and history happen to wind up with identical configurations. (One might argue that this would mess with the memories of living creatures in those universes - but if they have different memories to start with then the two universes can't merge because they are different. Only if every record of past history is somehow erased could two universes join back together. But because configuration space is 100% full of these snaking "narratives" - there are (paradoxically) exactly as many rejoinings as there are splits!

Now - what about time-travel? Well, when a creature who is in a universe that's winding through its narrative line decides to jump "back in time" - they take themselves to a point in configuration space where the universe has a bunch of particles representing the time traveller. That's close (in configuration space) to the narrative that the time traveller's universe passed along - but it's not the same. If the time traveller is super-careful not to kill his grandfather or do anything else to "change the future" (a very tough proposition!) then when he finally leaves the past to return to the present, the universe with the narrative that contains his particles in the past will eventually merge with the narrative of the universe he came from - and he will truly have "done no damage" to the present. If, however (much more likely!) he displaces an air molecule and that has a "butterfly" effect that causes greater and greater divergence of the narrative of this universe from the one he remembers - then perhaps the two narratives will never be able to rejoin.

It could also happen though that he could kill his own grandfather - thereby causing the "new" narrative to diverge still more from our own - but in a million years, the consequences of the time traveller never having lived might be utterly erased by the passage of time such that the original time-line and the new one would become identical in every respect - and rejoin.

But in this peculiar interpretation of the multiverse (which I find exceedingly compelling) - time travel not only might exist - but it definitely does exist - in the sense that somewhere in configuration space, there must be a universe where I suddenly pop into existance for no obvious reason with memories of being a time-traveller. Since all possible configurations "exist" - then for all practical purposes, time travel can happen even if the laws of physics prohibit it. Of course there are also versions of the universe where I pop back into a nearly identical narrative - but my ears have turned to lime jello...or the world of the "past" is entirely populated by giant intelligent pink rabbits.

This is a very weird view of the multiverse - but it's kinda compelling.

SteveBaker (talk) 12:51, 10 October 2008 (UTC)

true, an interesting model. and as you say, if all possible universes exist, then there must be an infinity of universes where time travel was invented, and the travelers spilled over into the neighboring universes. but that comes up against the next problem: the chances of us living in a universe where nobody pops up from a parallel where they invented time travel would seem to be close to zero; yet that's where we are. (inspired by the logic that since model universes can be created inside computers or such so much more easily and go through their life cycle so much more quickly that there must be so many more of them, that in all probability we would have to be in one of those, not in the "real" universe.)Gzuckier (talk) 05:48, 11 October 2008 (UTC)

I don't know that we can conclude that time travel "must" be common enough in the infinity of universes to say that we should expect to have seen time travellers. Also, I'm not suggesting that time travel can actually exist - it can't - the laws of physics don't allow that. What I'm suggesting is that the APPEARANCE of there being time travellers is perfectly possible - in the sense that (due to some quantum weirdness - or because Stephenson's model of configuration space is true) people could pop into existance with a complete set of memories that are clearly from the future and may indeed perfectly predict who will win the superbowl for the next 20 years. Such an event would be totally indistinguishable from real time travel. The John Titor incident is somewhat chilling though - he was pretty convincing as a time-traveller. This raises two difficult questions: Firstly, perhaps we HAVE been visited by a time traveller. Secondly, we didn't believe him - what makes you think we'd believe anyone who was a genuine time traveller? SteveBaker (talk) 01:45, 12 October 2008 (UTC)

The present exists. The future and past are both ideas. You can't travel to an idea. WAS 4.250 (talk) 20:30, 15 October 2008 (UTC)

Sterling Silver Allergy

If I were allergic to sterling silver jewelry, how long would I have to wear a ring around my finger to find out? 98.223.89.7 (talk) 02:32, 9 October 2008 (UTC)

I can't comment on sterling silver per se, but I can anecdotally report that my wife is allergic to gold. Its not the impurities in, say, 14K gold, its the gold itself. She's been tested an everything. The higher the Karats of the gold, the worse her reaction is. Even a few second contact with 24 karat gold gives her hives. So it is at least possible to be allergic to a metal like that. As far as how long YOU would take to break out, well, that depends entirely on YOU. Such facts of body chemistry are unique to each individual, and individual reactions cannot be predicted, especially over the internet. If you have questions about possible allergies you may have (and metal allergies are very real), you should see a dermatologist or an allergist and get tested. That is the only way to really know. --Jayron32.talk.contribs 02:43, 9 October 2008 (UTC)

This is interesting. How can an inert metal like gold (especially higher purity) trigger an allergic reaction? Sjschen (talk) 03:47, 9 October 2008 (UTC)

No idea on the mechanics, and if I had never seen it myself, I would not have believed it. We are both chemists by training, and understand the chemistry of gold. Gold is not entirely inert, and there is something there that triggers an allergic reaction in my wife. This is partially a wag, but there may be something about the surface texture of the gold that triggers the reaction; it may not need to actually dissolve into the skin, but the contact triggers a histamine response in my wife. Like I said, it shouldn't work that way, but I can only say that something about gold (and not the alloyants in lower purity gold jewlery, but the gold itself) that triggers the response in my wife. --Jayron32.talk.contribs 04:08, 9 October 2008 (UTC)

That's really interesting, especially as you can both take a scientific view on it. Have you tried double-blind experiments? Have you tried the experiment with and without her using whatever soap or lotion she uses on her hands? The latter to examine if the gold somehow acts as a catalyst. There apparently exist gold-based room-temperature catalysts for the oxidation of CO, for instance. EverGreg (talk) 08:28, 9 October 2008 (UTC)

I know that Gold can be ionized by a strong oxidizer such as conc. nitric acid, but I doubt sweat and lotions can do anything close to that. Maybe the gold catalyzed rxns in the lotion or soap is indeed the answer. Sjschen (talk) 22:28, 9 October 2008 (UTC)

Just as a totally apocryphal story, I once met a woman with a similar problem, but in her case it was lupus and not an allergy (she had a ring tattooed on her finger instead of wearing a wedding band because of a similar problem). My guess is that's more an issue of skin sensitivity and not the metal in itself. One option to test if it's a true allergic symptom is to see if it responds to antihistamines (i.e. diphenhydramine or somesuch), but it's more likely to be Contact dermatitis or some other sort of hypersensitivity than a true allergy. SDY (talk) 12:41, 9 October 2008 (UTC)

Yeah, your terminology is probably more correct than mine. I was probably using the term "Allergy" too broadly. The fact is that she has a reaction to gold (she has a platinum wedding band, and that causes no problems for her, and neither does silver or other costume jewlery), and whatever that reaction is is unpleasant for her, as gold causes an itchy rash. The solution for me is I just buy her cheap jewlery. Its a win-win situation for all of us!--Jayron32.talk.contribs 13:10, 9 October 2008 (UTC)

The original question actually asked how long to wear a ring until they find out. Well pure silver or gold is very weak and usually have alloys in it. Some people are very allergic and can only wear stainless steel, titanium, platinum, palladium, or tungsten, though sometimes I've read forum posts of people who're allergic to those, except I've never heard of a tungsten allergy. Also, there are some online sellers (often in China) who sell what they claim are sterling silver rings and they turn out not to be. Are you ready for IPv6? (talk) 13:53, 9 October 2008 (UTC)

(Not a RefDesk-quality answer...) Jayron, does this happen with other forms of gold, and on other parts of the body? Has she, for instance, "merely" set a gold coin on her arm and got the same reaction? Just curious. Maybe this should be moved to a talk page somewhere. --DaHorsesMouth (talk) 22:25, 9 October 2008 (UTC)

Jayron: I really think that if you are both scientists then a double-blind experiment is called for - and I'm very surprised you haven't already tried it. Too many scientists think that science ends at the laboratory door. A while back, my wife was spending a small fortune on bottled water - I maintained that she couldn't tell the difference between the cheap stuff and the expensive stuff - so we did a double-blind experiment. It turned out that not only could she not tell the difference between brands - but she couldn't even tell the difference between the good stuff and tap-water. That experiment saved us a fortune! In your wife's case, I think it's highly likely to be some kind of psychosomatic thing. Gold is just too inert to be a true culprit here. You need two similar sized rings - one gold, one of something else. It should be easy to figure out a double-blind methodology here - have one person take two small boxes labelled "A" and "B" and put one ring into each box - using a coin toss to decide which goes into which box and noting which was which - but not letting the other person know. Then the second person secretly does a coin flip and either swaps over the labels or does not (without looking inside). Then, both of you close your eyes - you pick out the ring from the box marked "A" and rub it onto her skin on her left arm - take the one from "B" and rub it onto her right arm - each time putting the ring back into the same box and closing the lid. Neither of you knows which ring was in which box until the results are in - then you can look into the box to find out - you should really do the experiment several times to be sure the result wasn't a flook. SteveBaker (talk) 04:10, 10 October 2008 (UTC)

Yeah, try this conversation on for size "Hey honey, you know that festering rash you get everytime you wear gold? Yeah, that really itchy shit that gets all pusy and nasty? Say, lets do that on purpose". I'll stick to buying her sterling silver jewlery and keep marital harmony going, thanks... --Jayron32.talk.contribs 04:22, 10 October 2008 (UTC)

I may have mentioned this before. I have a friend who has a weird reaction to gold, but only when she drinks alcohol. The skin around her wedding ring goes quite markedly blue. The whole ring finger and that side of her hand is affected. The skin touching her other jewellery or any other material does not do this. To prove the gold is playing some part, she once held a gold chain in the palm of her other hand while she was drinking wine, and her palm also went blue. She removed the chain, and the blue gradually receded, but the ring hand was still blue. It never happens when she's not drinking. I was spooked the first time I saw it. -- JackofOz (talk) 04:37, 10 October 2008 (UTC)

I have seen that before. That is generally due to the formation of copper compounds (which are blue) due to the presense of copper (as a hardener) in most gold jewelery alloys. Apparently, some people have skin chemistry capable of dissolving the copper out of these alloys. My wife has a very different reaction, which is distinctly either allergy, or dermatitis. --Jayron32.talk.contribs 04:45, 10 October 2008 (UTC)

I know you maintained that it was gold alone that caused your wife's allergy, but is she also allergic to nickel? a two-factor effect with gold + nickel could be one hypothesis. EverGreg (talk) 21:11, 10 October 2008 (UTC)

Perpetuating genes

Are there any known ways I can perpetuate my genetic stock without myself reproducing? Any that won't contribute to overpopulation? Also, are there any known ways of determining whether my genetic stock is above-average and worth making an effort to perpetuate? I have Asperger Syndrome, if that makes any difference. NeonMerlin 03:20, 9 October 2008 (UTC)

You could store your own semen. There are many sperm banks and other services that will do this for you. If you are female, you could also have eggs extracted and stored, but that involves invasive surgery, and is far riskier and less pleasant than the male method for extraction of reproductive genetic information. --Jayron32.talk.contribs 03:22, 9 October 2008 (UTC)

Note that the technology for long-term storage of unfertilized eggs is very new and has resulted in very few live births (I think I read about a first within the last year, but most IVF clinics don't do it yet). The exact reason why is not all that clearly understood, but freezing and the fertilization process don't work all that well together. Fertilized eggs can be stored easily, as can semen. SDY (talk) 08:47, 9 October 2008 (UTC)

You're asking some pretty tough questions, and it's hard to give suggestions here without bias. I suggest looking at genetic diversity, natural selection, and genetic testing to start you on the path to finding your own answers. Sjschen (talk) 04:01, 9 October 2008 (UTC)

An alternative is to support one's extended family as they have much the same genes as yourself. This is a tried and tested way of propagating genes in the animal world, with examples ranging from insects to mammals. EverGreg (talk) 08:34, 9 October 2008 (UTC)

This was what I was going to recommend. If your sister reproduces (if you have a sister), it's pretty similar genetic stock as your own, so at times it might be worth (from an evolutionary point of view) working to enhance her reproductive fitness even at the detriment of your own. See kin selection. --98.217.8.46 (talk) 11:20, 9 October 2008 (UTC)

As for "above average"... what do you really mean by that? You'd need to define your system of genetic worth first. It's not intuitive, and frankly we would probably disagree on what traits were most "desirable" and even some that were less "desirable". In the long run though your individual concerns about the worth of your genetics will play little role in the overall gene pool unless your reproduction rate is significantly differential from the average (either you produce more or they produce less). See eugenics. --98.217.8.46 (talk) 11:20, 9 October 2008 (UTC)

Although encouraging your relatives to reproduce will perpetuate your stock without your reproducing, it will still contribute to overpopulation. Theoretically, you could try to prevent other people from reproducing, but that would have a negligible effect on the portion of people who are related to you. Your only real solution is to go ahead and reproduce, and counter the effect on overpopulation by preventing others from having kids, or by increasing the capacity of the world. Because people in poverty reproduce more, I suggest donating to a charity that helps stop poverty, such as microcredit. If you donate a significant amount of money, it will be overkill, but I recommend that you do so anyway. — DanielLC 14:43, 9 October 2008 (UTC)

"Goodness" for a gene is really determined only by it's ability to spread and continue. Genes which don't make it into the next generation for some reason are "bad". So there is no way to indirectly measure goodness or badness of someone's genes. If they succeed in reproducing (preferably as many times as possible - and continuing for as many generations as possible) - then they are functioning well. A decision to not have children (no matter how socially good that is) is an indication that your genes have already failed in their goal to reproduce. Sooner or later, someone will come along with a higher sex drive or a higher maternal/paternal instinct that manages to overpower any hint of a desire to keep the earth's population in check. When that happens, their genes will spread faster than yours and your genes have failed and were therefore not as "good" as the ones that wiped them off the face of the gene pool. However, humans are (IMHO) gradually seeing more influence from memetic evolution than genetics. Memes are also able to propagate, evolve and reproduce - and in humans, a meme can have a greater role in driving us than our genes do. So perhaps the 'meme' that's telling us to save the planet is more powerful than the gene that's telling us to fill the planet from edge to edge with human beings. It is arguable, therefore, that you are doing a better job of passing on your best memes to the next generation than you are at passing on genes. So - become a teacher, or a writer or a musician - or merely answer questions on the ref desk in a way that reinforces the ideas (memes) that are worth passing on. SteveBaker (talk) 03:53, 10 October 2008 (UTC)

You might find Nature versus nurture an interesting read as well. SDY (talk) 15:05, 10 October 2008 (UTC)

in the Big Picture, you in all probability do not carry any genes which are not represented in the entire human gene pool at least several million times. and furthermore, if you did carry any rare mutations, the vast majority of them would be deleterious. so you can rest assured that even if you die without issue, your genetic components will not be lost to humanity. Gzuckier (talk) 05:41, 11 October 2008 (UTC)

Is our planet's core mostly iron because of boyancy?

?? 98.221.85.188 (talk) 04:18, 9 October 2008 (UTC)

Inner core is a pretty good read. One of the main driving forces behind the assumption that the core is mostly iron is that we know what everything else in the solar system is made of, and we know what our planet should be made of, and there's not nearly enough iron anywhere else on the planet to match the rest of the solar system. Ergo, the iron has to be somewhere, so its gotta be in the core. At least, that's how our article explains it. Its a fairly logical analysis of the situation. --Jayron32.talk.contribs 04:33, 9 October 2008 (UTC)

However, from the article Earth's magnetic field: Citing oceanic basalt 3He/4He ratios [5] and other evidence, J. Marvin Herndon et al contend that the inner core of the Earth is not iron but much denser atoms. --Ayacop (talk) 18:27, 9 October 2008 (UTC)

That's not what our articles say though. Our articles claim that the core is mostly Iron. And besides, what would these denser atoms be? 98.221.85.188 (talk) 14:37, 10 October 2008 (UTC)

Balancing equations

I can't for the life of me balance this equation: H₂S + SO₂ ---> S₈ + H₂O . The S₈ in the product's side is throwing me off! I thought I knew how to do this, until I attempted this problem. Can someone explain to me how to do this? I've been at it for far too long! —Preceding unsigned comment added by 134.241.222.116 (talk) 05:16, 9 October 2008 (UTC)

Note that that there must be twice as much H as O on the right. The S is just along for the ride. The coefficients are not low. I guarantee the equation will balance. Edison (talk) 05:30, 9 October 2008 (UTC)

In other words, if the left hand side of the balanced equation is AH₂S + BSO₂ where A and B are integers, then you must have A=2B in order to get the hydrogen and oxygen to balance, and also A+B must be a multiple of 8 so that you have a whole number of S₈ molecules on the right hand side. Gandalf61 (talk) 09:06, 9 October 2008 (UTC)

I still can't get it! Can you just tell me what it is? —Preceding unsigned comment added by 69.16.88.147 (talk) 11:15, 9 October 2008 (UTC)

Also note that, since A=2B, A+B=2B+B=3B. Since 8 is not divisible by 3, the fact that 3B must be a multiple of 8 implies that B itself must be a multiple of 8. In particular, the smallest value that could possibly be a solution is B=8. Why not try plugging it in and see if it works out? —Ilmari Karonen (talk) 11:45, 9 October 2008 (UTC)

To restate the above, since the water/SO₂ ratio requires there to be 3 sulfurs on the left side of the equation, and the S₈ is on the right, the answer must involve a number of sulfurs that is divisible BOTH by 3 and by 8. The lowest number that works for that is 24, so try to work out a solution that involves 24 sulfurs. That should put you in the right direction. An alternative method would involve solving this via the half-cell method. The reaction is a Synproportionation reaction, where sulfur in 2 oxidation states react to form a third oxidation state of sulfur. Track the oxidation numbers and see for yourself. You could try setting up two half-cell equations and balancing each and recombing them. This method is described here and an example is put forward here. If the brute force method using 24 sulfurs doesn't work, try the half-cell method.--Jayron32.talk.contribs 13:03, 9 October 2008 (UTC)

My recommendation to my students - ignore the requirement for integers until the end. After balancing the oxygen and hydrogen, you have 3 sulfur atoms on the left, with S₈ on the right. So you require 3/8ths of S₈. At the end, you can't have fractions, so then multiply everything all the coefficients by 8. I find this method a lot more intuitive than some of the above. --Bennybp (talk) 14:56, 9 October 2008 (UTC)

I think I got it! Is it 16-8-3-16? If so, thanks for all your help! If not, then I give up. —Preceding unsigned comment added by 69.16.88.147 (talk) 15:50, 12 October 2008 (UTC)

Yes, that's correct. It's easy to check; on the left you have 16×2=32 H, 16+8=24 S, and 8×2=16 O; on the right you have 3×8=24 S, 16×2=32 H, and 16 O. You're done! --Tardis (talk) 03:49, 14 October 2008 (UTC)

Ovulation

Why does the human body temperature increase whilst ovulating?90.210.162.166 (talk) 08:20, 9 October 2008 (UTC)

You may want to read Wikipedia's article on Ovulation. Having read it myself, I could posit an educated guess that ovulation is controlled by pituitary hormones, as mentioned in that article. The pituitary gland also controls metabolism and homeostasis in the body, and one of its main jobs is the regulation of your body temperature via metabolic control. My guess is that changes in body temperature are an indication that the pituitary is firing up in some way, which is a likely indication that it has released whatever the pre-ovulatory hormones are. This is largely a guess based on some intuitive readings of the articles on Ovulation and the Pituitary gland, but it makes sense to me. Does anyone else have a more concrete answer? --Jayron32.talk.contribs 12:52, 9 October 2008 (UTC)

From "Review of Medical Physiology" (William Ganong), the temperature rise at ovulation is probably due to the increase in progesterone secretion. Progesterone is thermogenic (i.e. increases metabolic rate and generates more heat). Axl ¤ [Talk] 18:03, 9 October 2008 (UTC)

True or False? Attack of the mutant 6 foot man eating catfist?

There is this story about a scientist who found a man eating catfish. As reported in the Newspaper.

http://www.thesun.co.uk/sol/homepage/news/weird/article1784470.ece

Is this story scientifically true? Ohanian (talk) 10:50, 9 October 2008 (UTC)

Well it certainly doesn't seem scientifically supported. All evidence given seems to be from what local natives and one reporter say—which generally means it is anecdotal evidence, the stuff of legend (no matter whether your locals are in India or Missouri). Personally I would want to see why the reporter fellow ruled out animals better known to have attacked humans in the past (crocodiles, snakes, etc.) before jumping to a new theory. --98.217.8.46 (talk) 11:10, 9 October 2008 (UTC)

Ha ha I read that as a scientist finding a man who was eating a catfish, rather than a man-eating catfish. I'd go with 98.217's reasoning, though a man eating a catfish would be pretty plausible - if not exactly newsworthy. 194.221.133.226 (talk) 12:29, 9 October 2008 (UTC)

The Sun isn't really world renowned for its fact-checking. APL (talk) 12:48, 9 October 2008 (UTC)

If you see the cover of The Sun at supermarkets, it's usually hypin some biblical prophecy that it says is about to happen. Are you ready for IPv6? (talk) 13:58, 9 October 2008 (UTC)

You should have put an "NSFW" warning on that. ;-) Axl ¤ [Talk] 18:07, 9 October 2008 (UTC)

I have seen catfish which weighed 50 pounds, and reliable witnesses have told of seeing larger ones living at the bottom of U.S. rivers just downstream from hydroelectric dams, eating the chopped fish who went through the turbines. As bottom feeders, catfish would certainly eat human bodies which had been placed in a river. All in all, it seems plausible but certainly not proved by a photo in a tabloid. I would have no trouble believing a report of one half the weight they claim. I could place a minnow that large in someone's hands in a Photoshopped picture. Seeing is not believing.

I don't know that much about catfish in general, but I can't quite imagine one eating a live human. I know that they would eat dead meat, so a dead human body wouldn't be that unlikely, but the live human...nonetheless, we could have a story about three 6 foot men eating a catfish, judging by that picture :-) Nyttend (talk) 22:01, 9 October 2008 (UTC)

6-foot and 161 lbs may be a record for that species of catfish but some species get much larger. The record Mekong giant catfish was "9 feet in length and weighing 293 kg (646 lb)." Rmhermen (talk) 23:42, 9 October 2008 (UTC)

Snopes has a couple of stories about huge catfish that may be of interest. Matt Deres (talk) 00:28, 10 October 2008 (UTC)

Quantum: why for entangled state but not separable states

I think there should be no difference between the entangled states and separable states (entangled states are just quantum states with special "pattern" and nothing else), so I speculate: if we measure one of the two entangled particle, the other will collapse instantly (just like this experiment), then how about measuring one of the two separated (non-entangled) particle? If we measure one of the two particle in separable state, does the other separated particle also collapse instantly? do whole of the other separated particles in our unverse collapse together with it (as the distance doesn't matter) simutaniously simultaneously and instantly? Can I say that all the other separated particles in our universe will actually collapse but just our sensor/device can't distinguish wheather whether they have collasped or not since they are in separable state? - Justin545 (talk) 12:07, 9 October 2008 (UTC)

Don't take too seriously the stuff about "the other particle collapsing instantly across arbitrary reaches of time and space." That's not something you can experimentally detect, it's just a feature of one particular mathematical formulation of quantum mechanics, and probably it should be taken to mean that that formulation doesn't correspond very well to reality. -- BenRG (talk) 21:34, 11 October 2008 (UTC)

Wave Function Collapse of Entangled Separable State

Suppose we have two particles $A$ and $B$ their respective states are

$|\psi \rangle _{A}={\sqrt {0.2}}|0\rangle _{A}+{\sqrt {0.8}}|1\rangle _{A}$

$|\psi \rangle _{B}={\sqrt {0.3}}|0\rangle _{B}+{\sqrt {0.7}}|1\rangle _{B}$

The state of the composite system of $A$ and $B$ is

$|\psi \rangle _{A}\otimes |\psi \rangle _{B}=({\sqrt {0.2}}|0\rangle _{A}+{\sqrt {0.8}}|1\rangle _{A})\otimes ({\sqrt {0.3}}|0\rangle _{B}+{\sqrt {0.7}}|1\rangle _{B})$

$|\psi \rangle _{A}|\psi \rangle _{B}={\sqrt {0.06}}|0\rangle _{A}|0\rangle _{B}+{\sqrt {0.14}}|0\rangle _{A}|1\rangle _{B}+{\sqrt {0.24}}|1\rangle _{A}|0\rangle _{B}+{\sqrt {0.56}}|1\rangle _{A}|1\rangle _{B}$

If we try to measure the state of particle $A$ of $|\psi \rangle _{A}|\psi \rangle _{B}$ and get state $|1\rangle _{A}$, it means $|\psi \rangle _{A}|\psi \rangle _{B}$ collapses to either $|1\rangle _{A}|0\rangle _{B}$ or $|1\rangle _{A}|1\rangle _{B}$. Besides, the probability of finding particle $B$ in state $|1\rangle _{B}$ is

$P\left(|1\rangle _{B}{\Big |}|1\rangle _{A}\right)={\frac {P(|1\rangle _{A}\cap |1\rangle _{B})}{P(|1\rangle _{A})}}$ (according to conditional probability $P(B\mid A)={\frac {P(A\cap B)}{P(A)}}$)

where

$P(|1\rangle _{A}\cap |1\rangle _{B})=P(|1\rangle _{A}|1\rangle _{B})=|{\sqrt {0.56}}|^{2}=0.56$

$P(|1\rangle _{A})=|{\sqrt {0.24}}|^{2}+|{\sqrt {0.56}}|^{2}=0.8$

therefore,

$P\left(|1\rangle _{B}{\Big |}|1\rangle _{A}\right)={\frac {0.56}{0.8}}=0.7=|{\sqrt {0.14}}|^{2}+|{\sqrt {0.56}}|^{2}=P(|1\rangle _{B})$

Similarly, if we try to measure the state of particle $A$ of $|\psi \rangle _{A}|\psi \rangle _{B}$ and get state $|0\rangle _{A}$, it means $|\psi \rangle _{A}|\psi \rangle _{B}$ collapses to either $|0\rangle _{A}|0\rangle _{B}$ or $|0\rangle _{A}|1\rangle _{B}$. Besides, the probability of finding particle $B$ in state $|1\rangle _{B}$ is

$P\left(|1\rangle _{B}{\Big |}|0\rangle _{A}\right)={\frac {0.14}{0.06+0.14}}=0.7=P(|1\rangle _{B})$

The above illustration shows that we are not able to distinguish whether the state of particle $B$ has collapsed or not, because no matter the state of particle $A$ we measured is $|0\rangle _{A}$ or $|1\rangle _{A}$, the state of particle $B$ always collapses to $|1\rangle _{B}$ with probability $0.7$. Therefore, we can say the particle $B$ DOSE collapse instantly (and so do all other particles in the universe) when we measure particle $A$, but we just have no way to emphasize that.

- Justin545 (talk) 06:06, 10 October 2008 (UTC)

what is the best way to structure a case study presentation on a medical patient ?

I have to present a case study to a large, mixed group of medical and allied-medical professionals. I have chosen my subject (the patient) and would like opinions on how best to structure and present the information and how to encourage discussion.Mollyisthedog1 (talk) 13:21, 9 October 2008 (UTC)

Are you planning to use Powerpoint? See "Medical history". Start with age & sex. Presenting complaint. History of presenting complaint. Past medical history. Drugs & allergies. Occupation. Social circumstances. Smoking & alcohol. Clinical examination findings. Relevant investigations. Treatment. Information about the specific disease. In smaller groups, I often invite individuals to comment on differential diagnosis and proposed management during the presentation. Axl ¤ [Talk] 18:16, 9 October 2008 (UTC)

Have you seen House (TV series)?

Just a thought, it may be worthwhile to present a brief abstract and overview before you plunge into details. Much of your audience will likely be used to reading journal articles, so following that structure (summary->methods->data->interpretation) will make the talk easier to follow for those familiar with the format. If the case study involves several cycles of "let's try this test, no that didn't work" it may make sense to have an overall summary, then do methods/data/discussion for each angle considered. SDY (talk) 15:03, 10 October 2008 (UTC)

solar power roof installations and having to do roof maintenance

Hi,

When you install a solar panel on your roof, and then have to replace the roof shingles for routine maintenance, how do the solar panels get in the way? Do you have to take the solar panels off, replace the shingles, and then reinstall the solar panels? What's the deal?

I feel irritated that all the solar roof websites I've read don't discuss this issue.

Thanks

--InverseSubstance (talk) 18:31, 9 October 2008 (UTC)

Hm. I don't know much about this, but perhaps calling one of the companies directly may get you a live person, who could answer any specific questions that you have? Its a start... --Jayron32.talk.contribs 19:20, 9 October 2008 (UTC)

Asphalt shingles are now available with rated lifetimes of forty years or more; steel roofing is often good for a hundred years. A properly designed and built roof that doesn't use low-quality shingles will almost certainly outlast the photovoltaic system on top. Proper installation of the solar panels may even slightly increase the lifespan of the roof by providing a small amount of extra protection from the elements. What type of 'routine maintenance' are you expecting to have to do that would require removal and replacement of shingles?

Interestingly, one can also purchase 'solar shingles'—photovoltaic panels which replace shingles altogether. TenOfAllTrades(talk) 19:33, 9 October 2008 (UTC)

The questioner could be asking about a solar water heater, and the removal of shingles might not be for maintenance of the shingles but maintenance of the roof structure. It's going to be hard to answer the question without knowing a lot more about the structure of the roof, how large the panel is, how and where it is located. It's good practice always to get at least three quotations for any kind of building work and the companies should be asked whether they have encountered a similar situation before and how they dealt with it. Itsmejudith (talk) 13:35, 10 October 2008 (UTC)

Ask your self something. How do they shingle around the various ventilation pipes protruding from the roof? The answer is you use flashing/and shingle around. So likewise, the supporting columns (for lack of a better word) for the solar panel would be shingled around.71.237.51.41 (talk) 19:59, 14 October 2008 (UTC)

Yes, and that's one disadvantage of a roof mounted photovoltaic solution. In lieu of the roof you could mount them on the side of the house or erect a pole in the yard and build a solar tracker. The roof mounted solutions block the sun so the roof will have less wear and tear.

I dont know shingles, but with ceramic tiles the solar electric panels are on an aluminium frame going through the roof. Then the tiles are cut just the same as the ones around the chimney etc. There is always an air gap between roof and panels, even if the roof angle is the same as the panels work less effeciently when hot. Working from the ceiling I suppose you could replace mostly from underneath. I'm not exactly answering your question, but the panel frames on the installations I've seen can always be unbolted (thieves do it). Polypipe Wrangler (talk) 21:42, 15 October 2008 (UTC)

Watch question

When was the jump hour function invented for clocks and watches? I imagine it must be quite old (here's a watch from the 1890s with the ability), but was curious. --140.247.42.160 (talk) 20:10, 9 October 2008 (UTC)

Unit of Measures

Would UOM KOhm be the same as kOhm —Preceding unsigned comment added by A01534 (talk • contribs) 20:27, 9 October 2008 (UTC)

I would think so. A lowercase k is the correct abbreviation for the SI prefix, "kilo-", but "K" is fairly common. I don't know anything else it could mean (in computing it sometimes means 1024 times, but that's non-standard). --Tango (talk) 20:54, 9 October 2008 (UTC)

I always found that slightly confusing. I had thought capitals were for "bigger" prefixes, and lower-case was for "smaller" prefixes. That seems to be the pattern most of the time - mega vs. milli, peta vs. pico, etc. But kilo, deca, and hecto don't. I guess it would be asking too much to be completely logical.... But yes, K probably means k in your question - there is no (SI) prefix for a capital K. --Bennybp (talk) 22:07, 9 October 2008 (UTC)

What you have to remember is that all the prefixes from milli- to kilo- are part of the original metric system while the ones from mega- upwards (and from micro- downwards) are later additions that have come in several batches over time. Presumably the forms "kg" and "km" were well established by the time that M- for mega- was introduced, and it wasn't until there were several more prefixes that the pattern of "higher prefixes get capitalized" was really established. So it makes sense that there was no pressure to change kilo- to be represented with a capital K. --Anonymous, 01:08 UTC, dekaOctober :-) 2008.

Along those same lines, the M- for mega- is also obviously influenced by the m- prefix already being in use. The next step there led to the use of μ- for micro-. Had more size prefixes started with k's, you'd likely see k-, K-, and κ- prefixes instead. Personally, I think using the Greek symbol was a dumb idea, but they no doubt didn't think of the hassle it was cause folks trying to use it on standard keyboards (and typewriters!). I would have gone with i- (for itsy-). ;-) Matt Deres (talk) 10:48, 10 October 2008 (UTC)

They probably rationalized it by assuming the letter 'u' could be used in place of the 'μ' without loss of clarity in typewritten documents. (No SI prefix uses upper- or lowercase 'u'.) Heck, I still use that shortcut—I've got Word set to autocorrect any instance of um to μm for me as I type.

I'd still say it's a better solution than the one adopted by some (mostly electrical) engineers. They use mm as a prefix (millimilli-) in lieu of mu, which is just asking for trouble. (Did you mean 1 mF or 1 mmF? Or do you want me to use a capacitor 1 mm long?) TenOfAllTrades(talk) 13:50, 10 October 2008 (UTC)

In fact the use of "u" in place of µ was officially approved by the ISO in 1974, but later withdrawn as character sets including µ became more commonly available. --Anonymous, 18:57 UTC, October 10, 2008.

See, all this confusion could have been avoided if they had just asked me in the first place! That way, at least I would have understood. (Of course I was only born in 1985, but that's what time machines are for!) :) --Bennybp (talk) 19:47, 10 October 2008 (UTC)

Then you'll appreciate what King Alfonso X of Castile (known as "Alfonso the Wise") said: Had I been present at the creation, I would have given some useful hints for the better ordering of the universe. -- JackofOz (talk) 20:28, 10 October 2008 (UTC)

"Ohm" as a unit of measure is not capitalized: hence "kohm". Axl ¤ [Talk] 18:57, 10 October 2008 (UTC)

Of course, if one were being pedantic, kohm is no more acceptable than kgram, kmeter, or kamp. It's either kΩ or kilohm. TenOfAllTrades(talk) 19:05, 10 October 2008 (UTC)

It would seem your spelling is correct, but what happened to the other 'o'? --Tango (talk) 19:10, 10 October 2008 (UTC)

It seems to be an arbitrary decision by the powers-that-be (I presume the BIPM). For ease of use, the doubled vowel was removed from kilohm and megohm (instead of using kiloohm and megaohm). A similar change was made with the are, giving us areas in hectares rather than hectaares. Not all double vowels are forbidden, however—kiloamperes and megaampere are cool. I imagine that there's a formal document spelling all this out somewhere, but I can't bring myself to hunt it down at the moment. TenOfAllTrades(talk) 20:14, 10 October 2008 (UTC)

Googling bipm.org reveals 3 instances of "kiloohm" and none of "kilohm". The SI brochure itself says nothing about removing vowels. It seems to me that the shortened forms, although widespread, are not sanctioned by the CGPM, but some national bodies like the NIST choose to define their own variants. --Heron (talk) 10:40, 11 October 2008 (UTC)

The SI standard only defines the symbols, not the spelling of the units (thus "m" is standard but corresponds to "meter" or "metre" in English, "mètre" in French, "Meter" in German, "metro" in Spanish, the Cyrillic equivalent of "metr" in Russian, etc.). National standards bodies may standardize the spelling of units, though. I don't know about the particular cases in question. --Anon, 21:48 UTC, October 11, 2008.

trying to remember the name of a certain stone

hi I have been trying to remember the name of a certain stone that we used to see alot of when we were kids. its a flacky stone that is black and foung in abundance in caves. i believed it was called "mika" but a search of it came up empty. the best way to describe it is that it usually comes in small or large chunks but can easily be split into little flakes and crumbles verry easily. If you could please get back to me it would be verry much apreciated. My email is [Redacted] —Preceding unsigned comment added by 99.241.82.198 (talk) 20:51, 9 October 2008 (UTC)

(I've removed your email address to protect you from spam - people will reply here.) I don't know much about rocks, so you'll have to wait for someone else to come along, but you can look through List of rock types and see if anything jumps out at you, if you like. --Tango (talk) 20:57, 9 October 2008 (UTC)

Mica? Saintrain (talk) 20:59, 9 October 2008 (UTC)

And if the variety you were seeing was black, Biotite. Deor (talk) 02:58, 10 October 2008 (UTC)

Another possibility is flint - but I was also thinking mica when I first read the question. Flint can be flaked, but mica is more "crumbly". Franamax (talk) 06:38, 10 October 2008 (UTC)

Venus axial tilt

Which one is right? Is Venus upside-down tilt axis of 177 degs, or normal upright of 2.6 degs. Old books say 2.6 degs axial tilt, but ewer study say Venus is upside down of 177 degs.--Freeway91 22:28, 9 October 2008 (UTC)

Either, they're the same thing. You can think of it as being tilted 177 degrees and rotating in the usual direction ("prograde"), or tilted 3 degrees and rotating backwards ("retrograde"). It doesn't really make any difference which you go with. (Although, interesting, our article says 177 degrees and retrograde, which doesn't sound right to me...) --Tango (talk) 22:36, 9 October 2008 (UTC)

Another way to view it is that "retrograde" means the axial tilt is greater than 90°, so "177° and retrograde" is a perfectly legitimate choice and in fact is probably the one I see most often. I don't know how professional astronomers describe it, though. --Anonymous, 01:11 UTC, October 10, 2008.

Then if Venus is rtro, then count it as 2.7 deg tilt. What about Pluto (which is no longer plnaet). If Pluto is rtro would it still be 120 deg. tilt?--Freeway91 22:51, 9 October 2008 (UTC)

Quantum Mechanics

Since quantum mechanics can't provide deterministic predictions, is it really falsifiable? And if it's not falsifiable, is it really a true science? 12.10.248.51 (talk) 19:02, 9 October 2008 (UTC)

The statistical predictions of QM are very much deterministic in the important ways, similar to Meteorology. In the place QM says things can not be determined (uncertainty principle) the theory puts a tight limit on the indeterminance(uncertainty) of its predictions. This aspect of the theory would easily be falsified by a theory being able to make a more accurate prediction. It might interest you to know that the prediction of QM explain many aspects of observations we make with chemical instrumentation. If we saw something different than what we do with NMR, EPR, UV-Vis, FTIR, Electroanalytical chemistry we would have to work on QM. This isn't to say QM is complete its just our best working theory. I've moved this to the reference desk since its a more appropriate place for the question and will receives explanations that far surpass this one.--OMCV (talk) 23:32, 9 October 2008 (UTC)

You can certainly falsify all sorts of aspects of it, even the stuff that appears almost purely philosophical at first glance. See, for example, the Bell test experiments. And the non-deterministic nature doesn't preclude testing or even predictions. Simple example: we have no way of making a "deterministic prediction" about when a single unstable atom will decay. But we can make statistical predictions which are easily testable (and thus come up with things like half-lives which are pretty iron-clad on the aggregate, even if they tell us nothing about the individual atom).

Note of course that Quantum Mechanics is the name of a field, not the name of a specific theory. Asking "can you test Quantum Mechanics?" is like asking "can you test Biology?" or "can you test Anthropology?" You wouldn't say a field was untestable unless the field's very definition excluded the possibility of naturalistic explanations (like Creationism). You can falsify all sorts of aspects to the theories that make up QM—it's been done since the 1930s, and is why we have the version of QM we have today and not many of the other versions that have been floated. (It's why we have something more like Bohr's version of QM rather than Einstein's, for example.)

There are some aspects of QM which are at the moment not falsifiable, in the realm of the metaphysical/philosophical interpretations of them. Whether those interpretations count as "science" would depend on who you asked and how you interpreted the term "science" in this case. But even then, sometimes they actually turn out to be falsifiable, like the issue of the EPR paradox, which was thought to be just a philosophical debate with no real testable content when it occurred in the 1930s, but in the 1970s it was discovered that there were very complicated but clever experimental setups that should be able to distinguish between some of the possible answers of it (the Bell tests I linked to earlier). --98.217.8.46 (talk) 23:58, 9 October 2008 (UTC)

October 10

Particle Physics

What is the difference between the Higg's boson and the graviton? They both are hypothesized to explain gravity, right? So how are they different? Ζρς ι'β' ^¡hábleme! 00:44, 10 October 2008 (UTC)

The Higgs boson is the unobserved member of the Standard Model that is supposed to explain inertial mass. The Standard Model does not deal with gravity at all. The graviton is the hypothetical force carrier for gravity within various theories of quantum gravity. Dragons flight (talk) 01:29, 10 October 2008 (UTC)

That's right. Sorry, I got the ideas cross for a second. Higgs deals with mass and the standard model, and graviton deals with gravity and hasn't anything to do with the standard model, really. Thanks, Ζρς ι'β' ^¡hábleme! 02:19, 10 October 2008 (UTC)

Turning off all electronic equipment during take-off and landing

Why are airline passengers instructed to turn off all electronic equipment during take-off and landing, even equipment that does not contain radio transmitters or receivers? I overheard a conversation recently, in which a fellow passenger claimed that it is done to ensure that people pay attention to what is being said over the loudspeakers, in case of emergencies during the most critical parts of a flight. Can anyone confirm this, or suggest other reasons for this requirement? --NorwegianBlue ^talk 11:07, 10 October 2008 (UTC)

I've heard the same reason (on numerous ocassions) as you suggest. LIke you say it ensures people are not distracted if there is a need to make an annoucement/emergency decisions. I have been told to stop reading my book before so I would suggest it is more about paying attention than it is about anything else. 194.221.133.226 (talk) 11:19, 10 October 2008 (UTC)

In the past it could have been do to with interference (even without transmitters any electronic equipment will emit some EM, I believe), but I'm pretty sure all critical systems on planes are shielded these days. As such, it is probably just to make sure people pay attention and, if not, at least don't make too much noise stopping other people from hearing announcements. On a related note, the reason you aren't allowed to use mobile phones in hospitals is simply because it annoys people, it's been a long time since medical equipment was sensitive to such things. --Tango (talk) 11:21, 10 October 2008 (UTC)

In general it's both. EM interference is a legitimate risk (though a much smaller one than when the rules were written in the 60s and 70s), and it is easier to swtich off all electronics than have flight attendents try to figure out which ones actually need to be disabled. At the same time, the FAA also cites the "possibility of missing important safety announcements during these important phases of flight" [5] as an additional reason to turn off electronics during takeoff and landing. Dragons flight (talk) 11:32, 10 October 2008 (UTC)

Note as well that handheld electronics represent dangerous projectiles in the cabin in the event of a crash. Headphone cables can present a tripping hazard. On takeoff and landing, the cabin crew want you to stow everything securely, not just electronics. TenOfAllTrades(talk) 13:30, 10 October 2008 (UTC)

The turning off electronics thing is just to "make sure", but realistically there's no point. If turning on an electronic device could really interfere with the cockpit's electronics, then terrorists would have a field day. 98.221.85.188 (talk) 14:41, 10 October 2008 (UTC)

The initial justification, Crossair Flight 498, was pretty lame since there were other confounding factors involved. That said, I can hear my speakers making odd noises when I point my cell phone at them the right way, and if I were talking to a control tower to avoid smacking into somebody at 400 knots, I think I'd rather the pilot have a clear signal. SDY (talk) 14:51, 10 October 2008 (UTC)

Your speakers (and the cables attached to them) aren't shielded from EM interference, I would hope the flight deck radio is. --Tango (talk) 15:10, 10 October 2008 (UTC)

How does that work with wireless communication, though? Then again, I'd imagine that the cell phone bands are all quite separate from the bands that aircraft use. SDY (talk) 15:18, 10 October 2008 (UTC)

Is anything in planes wireless? The computers they use for duty free transactions might be, but that's hardly a critical system! --Tango (talk) 15:27, 10 October 2008 (UTC)

Many planes have satellite radios, satellite TV, etc. for the passengers. Not to mention all of their telemetry equipment that is used to monitor where the plane is, how it is flying, etc. by flight control. --98.217.8.46 (talk) 15:49, 10 October 2008 (UTC)

The thinking is that if some of the electronic equipment onboard had been stripped of shielding (say, by shoddy maintenance) then your electronics could interfere. Of course, the plane has a high-voltage radio of its own, which would produce a thousand times more interference than your iPod. It is a dumb rule, but lots of these FAA rules are. They are rituals meant to make you feel safe, not actual safety measures. The lifejackets are a great example. How long do they spend teaching you how to put on a lifejacket? "Your life jacket is located under your seat, or under the arm rest between the seats. Pull the life jacket over your head and attach the strap. Infant life jackets will be distributed, if required. Do not inflate your jacket until you leave the aircraft. Pull the strap until the jacket is properly adjusted. If the life jacket does not inflate or needs more air, blow through the rubber tube." It's a nice image, you bobbing safely in the water with a bright yellow life jacket on. How many people have they actually saved? Zero. Meanwhile hundreds of people die from smoke inhalation which can be prevented by a lightweight mask. There is no rhyme or reason. Plasticup ^T/C 16:05, 10 October 2008 (UTC)

Are you sure of that number? I'm aware of several water landings where there were survivors; are you saying that in none of the cases were life vests used? --Carnildo (talk) 22:32, 10 October 2008 (UTC)

They shouldn't have been used if the evacuation went as planned since everyone would be in inflatable life rafts. Of course, if you're making a water landing, things aren't exactly going to plan, so... --Tango (talk) 23:14, 10 October 2008 (UTC)

Carnildo, for my interest, could you point to a water landing where there were survivors? My impression is that no commercial (large) jet passengers have ever survived a water impact. Skidding off runways, yes, but not "crashes". I'd be interested in the details. Franamax (talk) 00:58, 11 October 2008 (UTC)

See Ditching#Survival Rates of Passenger Plane Water Ditchings. From the article this crash] had 52 survivors. - Akamad (talk) 02:19, 11 October 2008 (UTC)

And more specifically, Ethiopian Airlines Flight 961, although I'm under the impression that life jackets actually killed more people than they saved in that particular incident. --antilived^{T | C | G} 05:12, 11 October 2008 (UTC)

Seen another way, improper use of life jackets caused loss of life, because people inflated them prior to exiting the plane, which is directly contrary to standard instruction. Maybe the relatively protracted training reflects the complexity of using these devices properly. Perhaps they should spend more time on when to inflate than how to inflate. --Scray (talk) 15:02, 12 October 2008 (UTC)

They usually say the standard, 'pull one just before you leave the plane, pull the second one after you leave' whenever I've been in a plane, that I recall anyway. Also, I think your summation is more accurate. We don't actually know whether it costs more people their lives then it saved. It's possible many of those who survived would have died without lifejackets and many of those who died would have died anyway. Nil Einne (talk) 13:16, 13 October 2008 (UTC)

coincidentally, yesterday:

Safety investigators will now ask passengers if they were using any electronic equipment at the time of this latest incident. "Certainly in our discussions with passengers that is exactly the sort of question we will be asking - 'Were you using a computer?'," The Courier Mail quoted an Australian Transport Safety Bureau (ATSB) spokesman as saying. The ATSB said the pilots received messages about "some irregularity with the aircraft's elevator control system", before the plane climbed 300 feet and then nosedived. [6] but apparently they've decided laptops were innocent.

that article does contain the following surprising (to me) sentence, though: In July, a passenger clicking on a wireless mouse mid-flight was blamed for causing a Qantas jet to be thrown off course, according to the Australian Transport Safety Bureau's monthly report. Gzuckier (talk) 05:33, 11 October 2008 (UTC)

Thanks, everyone, for your responses! --NorwegianBlue ^talk 12:52, 11 October 2008 (UTC)

This one on the same incident also mentions modems and previous cases [7] Nil Einne (talk) 13:12, 13 October 2008 (UTC)

Now seems that in the specific case that brought all this to light, it wasn't interference [8]

problem sum

a constant retarding force of 50 newtons is applied to a body of mass 20 kilograms moving initially with speed of 15 metres per second. how lomg does the body take to stop —Preceding unsigned comment added by 77.31.137.209 (talk) 16:22, 10 October 2008 (UTC)

Not that we should solve homework problems for you, but consider that a newton is a kilogram meter per second squared (kg*m/s²) and simple factor label cancelling (i.e. do the algebra with the units to figure out how to multiply and divide the numbers) should give you the answer. The article I linked shows the basic framework for solving problems like this. --Jayron32.talk.contribs 16:51, 10 October 2008 (UTC)

While I would probably do the same as you, the more standard approach is the learn the constant acceleration formulae. Pick the appropriate one of them along with F=ma and substitute in the numbers. --Tango (talk) 16:58, 10 October 2008 (UTC)

True, but that requires one to either memorize a list of formlas, or to be able to work the calculus on one formula to derive the rest. The nice thing about the factor-label method is that it requires learning a single method that is broadly applicable accross MANY fields. It will get you the right answer, for example, in any high school or introductory collegiate chemistry and/or physics class for, quite literally, 90% of the homework problems you will get. One method, 90% of the problems. The "learn every formula method" also works, but is, IMHO, more labor intensive and time consuming. --Jayron32.talk.contribs 17:33, 10 October 2008 (UTC)

Couldn't agree more, but it's generally best to help someone get to grips with the method they're being taught (which is almost certainly the memorise formulae method) rather than teaching them a whole new method. --Tango (talk) 19:01, 10 October 2008 (UTC)

You've all forgotten that the dimensional analysis, while certainly very useful, is no substitute for knowing why you're multiplying things in the first place--it's simply a way to check that you haven't combined units in a nonsensical way. For example, for energy stored in a spring, you may be tempted to use U = kx^2, when the formula is actually (1/2)kx^2. If you were to merely use dimensional analysis you would arrive at the wrong answer. Actually, the best way is to learn everything, including the calculus behind it. Then you'll never have any doubt as to whether the formula has a 1/2 or not; just do the integral. --M1ss1ontomars2k4 (talk) 21:03, 11 October 2008 (UTC)

Actually, you don't even need calculus to get the constant acceleration formulae, you can work them out geometrically from distance/time and velocity/time graphs (well, I guess you could say it's calculus because you need to know how to interpret the area under the curve, etc., but you don't actually need to integrate or differentiate anything). But you are correct that the method does mean you are occasionally out by a factor of two (it's always two...), but I generally ignore factors of two, they're rarely important! ;) --Tango (talk) 22:56, 11 October 2008 (UTC)

threshold logic synthesis

can anybody help me to know how to find the false vertices for threshold logic synthesis....... —Preceding unsigned comment added by Sveta rathi (talk • contribs) 19:04, 10 October 2008 (UTC)

Wikipedia has an article on Logic synthesis that also has a long list of referenes and other links at the end. This may be a good place to start. --Jayron32.talk.contribs 19:20, 10 October 2008 (UTC)

"Virgin birth" in a shark

http://ap.google.com/article/ALeqM5gV-UePymWuPU7HFxNgUXRUrakU1wD93NPTM80

How did this exactly happen? Can the same thing happen to humans? --Emyn ned (talk) 20:07, 10 October 2008 (UTC)

The process is called parthenogenesis. (Our article discusses the matter in some detail.) Briefly, there's never been a substantiated case of parthenogenesis in any mammal (including humans) in the wild. Induced parthenogenesis has apparently been demonstrated in rabbits and mice, producing viable offspring. Human parthenogenesis has been demonstrated to the extent of creating human embryonic stem cells from unfertilized eggs, though no human beings have been born via this method. TenOfAllTrades(talk) 20:22, 10 October 2008 (UTC)

it's not too hard to make an egg cell of any animal start to divide, even if not fertilized; it's all caused by a bunch of calcium entering, calcium being a handy ion in organisms for signals like that, it's not too scarce like magnesium and not too abundant like sodium. The chromosomes provided by the sperm actually don't have anything to do with triggering the egg's development, but the whole thing is set up that the arrival of the sperm triggers that calcium influx which starts the division, and the arrival of the chromosomes in the same package is basically a happy accident. but you can trigger the calcium influx via drugs and things in eggs of many species and away they go. once the cell starts the process of dividing and then duplicating chromosomes and dividing again, the fact that it only has one set of chromosomes instead of two gets fixed as that set gets duplicated after a cell division. (the other product of the division has no sets of chromosomes, and just sort of fades away, but that's not a problem; cells early in the division process aren't specialized yet, each one can produce a complete embryo if they're separated, that's where identical twins come from.) so at that point you've got a dividing egg cell with two sets of chromosomes, and you're on your way. the fact that both sets are identical isn't critical, but of course any undesirable recessive genes will pop up.

in sharks? well we're seeing a lot of it now, because we didn't look for it before, so it's likely that some mechanism has evolved which can trigger the egg reasonably frequently without the need for sperm. there are other species which don't have males at all, of course, so this is just a less emphatic version of that. might happen occasionally in other animals too; people for instance. it would be hard to prove, particularly if it was pretty rare. there is this one story about a virgin, a couple of thousand years ago.... Gzuckier (talk) 20:29, 10 October 2008 (UTC)

It could happen in humans, I believe. Unfortunately or fortunately, only females would be produced in such cases, due to the XY sex chromosome thing. Imagine Reason (talk) 04:15, 11 October 2008 (UTC)

i really should know this but

how do volumes add in a liquid solution? i know all about partial pressures, etc. but if 10 ml of alcohol is added to 90 ml of water, is the result 100 ml? how about when dissolving solids in a liquid? thanks. Gzuckier (talk) 20:18, 10 October 2008 (UTC)

Unfortunately, there's not a simple answer to this one. In general, the volume of a solution will not be equal to the sum of the separate volumes of its components. In other words, if you add 10 mL of ethanol to 90 mL of water, the final volume will come out to be slightly less than 100 mL (about 99.5 mL, actually). This discrepancy will depend on the compounds being mixed, and on their proportions. (If you add 40 mL of ethanol to 60 mL of water, the final solution will be a shade less than 98 mL volume.) Dissolving solids in liquids has similar problems.

Conceptually, you can think of the molecules of solute being able to at least partially occupy gaps left between the loosely-packed solvent molecules, but that's an awfully hand-waving description. TenOfAllTrades(talk) 20:44, 10 October 2008 (UTC)

As a more detailed description, consider that there is in the individual pure liquids, the macroscopic "volume" property is determined by a microscopic property we can call "intermolecular distance" that the molecules seperate themselves by. So, there is a water-water intermolecular distance and a ethanol-ethanol intermolecular distance. When you mix the two, you create a new interaction, the ethanol-water interaction, which is a shorter distance than either the ethanol-ethanol or water-water distance. This makes sense if you consider that in order to for two substances be miscable, the molecules of each substance must be more attracted to each other than to themselves.(if the water and ethanol were more attracted to themselves than to each other, then the two would merely aggregate seperately, and would not mix). More attractive force means shorter distance between them. So a solution of two substances should always occupy a smaller volume than the sum of their pre-mixed volumes. --Jayron32.talk.contribs 23:13, 10 October 2008 (UTC)

That's a completely different description. The first one is wrong, and just happens to partially explain a little. — DanielLC 16:22, 11 October 2008 (UTC)

Wow. I mean, really? Come on guys, let's keep our feet on the ground. Yes intermolecular forces in the solution will increase with the presence of a solute (except when combining immiscible solutions), but the resulting change in volume is unnoticeable unless you have spectacular equipment or a tremendous amount of material. When you add salt to water the melting point may drop but the volume does not, even though the packing of molecules in the liquid changes significantly. For all intents and purposes the OP's original intuitions are correct: 10ml EtOH + 90 ml H2O = 100ml. The only real concerns with respect to change in volume when adding liquids is whether or not they'll react, causing product to evolve out of solution or causing the temperature of solution to change. --Shaggorama (talk) 05:02, 13 October 2008 (UTC)

Er no, really really, the OP asked whether volumes add, and gave an example. The answer is no, they almost never exactly add, and in particular it's "close but not quite" for the example given. The why is a different story, but volume of mixing is a real phenomenon (and can be greater or less than the sum of the parts). Mixing a solute into a solvent and looking for change in solution (vs solvent) volume is indeed often a small deviation. But still, that's just a question of temperature whether the solute is solid or liquid, not something about the solution. You can dissolve a heck of a lot of sugar in water and only get a marginal increase in volume, which just proves that volumes often don't add, even approximately. DMacks (talk) 05:11, 13 October 2008 (UTC)

There seems to be a pretty clear consensus here so maybe I should just sit down and shut up, but I've taken chemistry through college level orgo and the phenomenon at hand never reared its ugly head. I maintain that for all intents and purposes it can be ignored. Unless the op is in a high level course (in which case they certainly wouldn't be asking this question) then the phenomenon can certainly be ignored for the purposes of performing ceteris peribus chemistry math on paper. Furthermore, the quantities of solution and necessary significant figures they will be using in lab preclude concerning about it there. I'm not denying that the phenomenon exists, I'm arguing that :

1. it's not even close to as significant/noticeable as has been suggested, and
2. we should therefore be advising the op not to worry about it and do the math intuitively since that's what they'll be observing in the real world.

Dmacks, I don't know where you're going with the sugar example. I introduced the salt example to illustrate that intermolecular forces do not cause significant decrease in volume, as had been suggested earlier. That adding solid solute offers effectively no change to volume, as you pointed out in the sugar case, lends support to my stance. I hadn't suggested that solid + liquid adds the same way as liquid + liquid. Feel free to elaborate if I misunderstood. --Shaggorama (talk) 06:16, 13 October 2008 (UTC)

I think you did understand but maybe are seeing a false dichotomy. There are indeed two issues: does solvent volume change when a solute is added and does the total volume change add when two volumes are mixed. Common experience says "little if any" to the first (salt or sugar in water) and "approximately yes" to the second (alcohol plus water). But wait...those are contradictory positions! If adding solute doesn't much affect the solution volume, the solute acts as if it has no volume of its own. Otherwise, if adding a volume of solute increases the solution volume by its volume, then the whole intermolecular-attraction and fills-in-the-spaces idea is wrong. Now here's where I think you misunderstood. There's no intrinsic difference between "chemicals that are solids" and "chemicals that are liquids", and there's no memory once in solution whether the solute happened to have been a solid or liquid. Solid+liquid vs liquid+liquid is just a matter of whether the experiment is done at a high enough temperature that the solute melts. I picked sugar just as a parallel example to salt, but as something that can be melted easily to ponder whether "physical state" matters. DMacks (talk) 06:44, 13 October 2008 (UTC)

You make a good point and I'm inclined to agree with your reasoning, but that doesn't make the phenomenon itself any stronger. You could never actually add liquid sugar to liquid water because sugar melts above water's boiling temperature. Once you dissolve sugar to add it to pure water as an aqueous solution, you're end result is still mostly water and the volumes will add intuitively. Perhaps I should have qualified my rule-of-thumb for aqueous solutions, but I'm fairly certain it holds true in hydrophobic solutions as well. I'm inclined to agree with you on the "false dichotomy" you pointed out, but in empirical terms solids that dissolve in water do not significantly change the volume of solution, and liquids do (maybe because they are solutions in water). --Shaggorama (talk) 07:16, 13 October 2008 (UTC)

How about trying to mix some liquid water with alcohol at just above  °C and mixing that same amount of water as ice with the same amount of alcohol at just below  °C until they dissolve, then compare the volumes. DMacks (talk) 19:10, 13 October 2008 (UTC)

What is the movement of a submarine called?

Sailing? Driving? —Preceding unsigned comment added by 87.165.220.170 (talk) 20:55, 10 October 2008 (UTC)

'Sailing' appears to be a widely-used, widely-accepted term. (Google submarine sailed or submarine sailing to see many, many examples of usage.) 'Driving' is definitely not. TenOfAllTrades(talk) 23:30, 10 October 2008 (UTC)

It's odd that, for ships, at one time "sailing" was updated to "steaming" but now seems to have reverted to "sailing" even though the technology has gone somewhere else entirely. I guess dieseling, electricking or nuclear reacting just don't roll off the tongue. SpinningSpark 12:41, 11 October 2008 (UTC)

So we sailed up to the sun . . . in our yellow submarine - Lennon-McCartney

Sudden moon

I am writing a story set on a planet that has suddenly acquired a moon. For the purposes of this question, just assume it suddenly appeared and that both the planet and moon are the same size as ours.

I'm trying to work out exactly the nature and scale of the disasters this would cause. All I've got so far are extreme tidal waves and flooding, but would there also be earthquakes? I think it would probably result in massive unbalancing and possibly death among nocturnal species, not to mention the probable extinction of a lot of tidal zone species. What else, though?

While I'm at it, what would a world be like that did not have a moon? It would have very small tides thanks to the sun, and would always be very dark at night... One of my friends claims that it wouldn't have seasons, but I find that dubious. Any thoughts? --Masamage ♫ 21:12, 10 October 2008 (UTC)

I don't think you would get anything more drastic that we get every day, since as the Earth rotates different parts of the Earth are affected by the moon's gravity (you might get some problems immeadiately after the arrival since you would have the effect of 6 hours worth of tidal change in an instant [although the magnitude of the tides would be the same as for the Earth], but that wouldn't last long, although the damage from it might). The fact that life wouldn't be used to the tides would be a problem, certainly, but I think that's about it (and remember, it's just increased tides, not new tides, because of the sun). As for a planet without a moon, it would probably affect the seasons, but it wouldn't preclude having them. Seasons are caused by the rotational axis being tilted with respect to the orbit, the moon may well have affected our axial tilt, but having a moon isn't a requirement to have one. The day would also be shorter, since the same tidal forces which mean the moon always shows the same face to Earth are gradually slowing the Earth's rotation, without the moon that wouldn't have happened so the day would be a few hours shorter (I'm not sure how many, but I believe it's been measured by looking at fossilised coral). I read somewhere that the moon has helped stabilise the Earth's rotational axis, but I'm not sure how, so the seasons may be more variable without a moon (although probably on the scale of centuries at least). --Tango (talk) 21:31, 10 October 2008 (UTC)

Instantaneous appearance? You'd get at least the following:

1. A sudden shock as the planet shifts from following a simple orbital path around its sun to the sine-wave pattern the Earth follows. (The center of gravity of the Earth-Moon system follows an elliptical path around the Sun; the Earth and Moon orbit that center of gravity with a period of one Lunar month).
2. Gradually-increasing tidal heights, with the final tidal range being about three times what it used to be. Timing of the high tides will also change. You won't get tidal waves because the water has a long way to flow to adapt to the new gravity patterns, and it doesn't move very fast. At a guess, it'll take a month or two for the tides to reach their final heights.
3. More earthquakes. They won't be stronger, and they might be weaker, because of increased tidal flexing of the crustal plates.
4. Disruption of activity for many species: some night-active species will have trouble being active during full moons; some day-active species will stay active at night during full moons.
5. Increased predation of day-active prey species. The increased night-time lighting means that camoflage patterns and sleeping habits are no longer adequate for protection. It'll take about five years for the resulting boom-and-bust of night-active predator species to settle out.

Over the long term, you'd see the following:

1. More reliable seasons. Adding a large moon will stabilize the planet's rotation axis, so the strength of the seasons won't change over time (millions to billion of years)
2. An increase in the number of night-active species. More light means it's easier to move around at night. (hundreds to tens of thousands of years)
3. A reduction in meteor impacts: the Moon provides some protection against meteors by variously blocking them, causing them to break up, or throwing them out of Earth-crossing orbits.
4. An increase in volcanism: the increase in tidal flexing will increase the temperature of the planet. (Hundreds of thousands to millions of years)

Hope this helps. --Carnildo (talk) 22:58, 10 October 2008 (UTC)

If you are interested in this subject, and want to see how another author has treated a similar situation (though not exactly the same), may I recommend Jack McDevitt's book Deepsix, it has some interesting descriptions of weird tidal effects caused by two large planets on a collision course. Its part of his "Priscilla Hutchins" series, and is an enjoyable read. --Jayron32.talk.contribs 23:05, 10 October 2008 (UTC)

Why would it take months for the tides to reach their maximum? The water doesn't need to move any faster than it does on Earth and it can go all the way round the Earth in 24 hours (well, individual bits of water don't, but you know what I mean). --Tango (talk) 23:13, 10 October 2008 (UTC)

On Earth, the tides have had billions of years to build up momentum. The Moon's gravity isn't very strong, so the water doesn't accelerate very fast. --Carnildo (talk) 23:29, 10 October 2008 (UTC)

That's utter nonsense.

The water oscillates back and forth twice per day. So the momentum builds up slowly over about six hours then back the other way over the next six. It doesn't "build up" over millions of years. The tides would settle into their regular pattern in about a day or two. I think there could be no earthquakes or anything because the earth too squeezes and stretches in a cycle over 12 hours and we don't see particular problems because of that. I agree though that the SUDDEN arrive of a few gigatons of stuff in orbit would very abruptly jerk the planet in it's orbit - and that would be utterly disasterous - all of the oceans and atmosphere would slosh violently - possibly flying off the planet completely...it's hard to imagine any life surviving that. But if the moon somehow slowly spiralled into position over decades - then I think it would have fairly benign effects (well, crazy weather - tides where they'd never been before - flooding, rivers running backwards...but definitely something you could survive). You'd also have to consider the consequences of the moon suddenly being dumped into the much stronger gravity well of the planet. Since we have no knowledge of the "magic" that makes the moon suddenly teleport into place - we can't guess what forces that entails - but it might well break up, ending up as a truly spectacular ring system...or possibly raining death and destruction onto the surface. SteveBaker (talk) 01:12, 11 October 2008 (UTC)

The change in orbital motion would not cause a "shock"; each planet is in free fall, and would continue falling freely even if in a different direction. The only "sudden shock" would be from tides: expect a lot of earthquakes at first. —Tamfang (talk) 01:39, 14 October 2008 (UTC)

hydrogen reaction

Will a balloon filled with pure hydrogen and pierced with a needle made of palladium explode/combust? —Preceding unsigned comment added by Kaufmann1 (talk • contribs) 21:57, 10 October 2008 (UTC)

Not unless the palladium is particularly hot. Palladium can act as a catalyst for certain reactions involving hydrogen, however as far as I am aware, it does not lower the activation energy of the combustion reaction enough to cause it to become spontaneous. --Jayron32.talk.contribs 22:56, 10 October 2008 (UTC)

Pure hydrogen? What would it react with? --Carnildo (talk) 22:58, 10 October 2008 (UTC)

The oxygen in the atmosphere outside the balloon, presumably. Algebraist 23:05, 10 October 2008 (UTC)

Our article on palladium says it can absorb large amounts of hydrogen. I'm not sure if that reaction releases energy, but I doubt it would do so to the extent of causing an explosion. --Tango (talk) 23:10, 10 October 2008 (UTC)

Where can I get a palladium needle, to try the experiment? Edison (talk) 19:30, 11 October 2008 (UTC)

You would probably have to turn it into a needle yourself, but you could buy a palladium coin here (for about $200, although they're out of stock apparently...). --Tango (talk) 22:51, 11 October 2008 (UTC)

However, a needle or other solid form is just about the worst you can do if you're trying to get a rapid reaction. The reaction between a gas and a metal (or "chemical adsorbed or absorbed onto/into the metal" happens at the metal surface, so the bulk of the solid metal below the surface is useless. Much better to use powdered Pd (or Pd coated on some other powder) or a porous matrix. The large surface area allows much more rapid reaction. I've seen active metals like Pd and Pt supported on powdered charcoal--the form commonly used for lab-scale catalytic hydrogenation reactions--lead to combustion with atmospheric oxygen even without substantial hydrogen present (I'm sure helped by the charcoal being flammable). DMacks (talk) 18:46, 12 October 2008 (UTC)

Mars climate

How does climates on Mars work?Does temperats range by latitudes, seasons or night-and day. Ithouhgt Mars is a very cold planet, often colder than a freezer, and the average planet temp is around minus 67 F. Is that the mid-latitude average surface temp? I thought only tropical zones of Mars or low latitudes get temp range from +10 to +69 F.--Freeway91 22:15, 10 October 2008 (UTC)

Interestingly, we have an article on that: Climate of Mars. --Jayron32.talk.contribs 22:58, 10 October 2008 (UTC)

The variation of temperature with latitude, seasons and day/night don't really depend on the planet so much as how it moves around the sun. Pretty much all of the planets have all of those things (with the sole exception of Mercury which keeps the same face pointing towards the sun all the time - so it doesn't have day/night cycles).

• Variation by latitude is because the planet is round and the sun's rays spread out more at the poles than at the equator.
• Variation by season is because most planets are doing their daily rotation about an axis that's tipped over somewhat. This means that the suns rays are more spread out at some times of the year than others. For planets with very elliptical orbits, there is a variation due to distance from the sun too.
• Variation between night and day is because the sun isn't shining on the surface at night.

So all of those things vary on all planets that are round, have an axial tilt and rotate on their axis...and that includes Mars.

SteveBaker (talk) 00:47, 11 October 2008 (UTC)

Actually, Mercury isn't tidally locked (although astronomers did think it was at one time). See Mercury (planet)#Spin–orbit resonance. --Tango (talk) 00:55, 11 October 2008 (UTC)

Seconded. Apparently Steve is stuck in 1964;-) --Stephan Schulz (talk) 01:01, 11 October 2008 (UTC)

In more ways than you can imagine! SteveBaker (talk) 01:20, 11 October 2008 (UTC)

So isn't temperate zone on Mars lattide of 30+ always or often below 0, and lattitude of 50+ alwas colder than Greenland? Generally, Mars I thought is very cold.--Freeway91 01:04, 11 October 2008 (UTC)

Because of its thin atmosphere it doesn't retain heat well, so at night it is going to be extremely cold regardless of your latitude. During the day, it will be warmer the nearer the equator you are (well, not quite the equator due to the axial tilt). I don't know any numbers off the top of my head, but they shouldn't be too difficult to find with a bit of googling. --Tango (talk) 13:53, 11 October 2008 (UTC)

October 11

gas constant?

why should we use a constant for gas equations?where does the universal gas constant come from?i couldn't find any information about history of gas constant(R)? —Preceding unsigned comment added by 88.242.106.180 (talk) 00:57, 11 October 2008 (UTC)

You may want to have a look at gas constant and Boltzmann constant for a more detailed treatment of the topic. Briefly, the gas constant (R) is a proportionality constant which describes how much energy is stored in a mole of (ideal) gas molecules per degree of temperature. (The related Boltzmann constant, k_B, describes the quantity of energy per molecule.) TenOfAllTrades(talk) 01:40, 11 October 2008 (UTC)

A pity nothing is said in the articles about experiments like in de:Universelle_Gaskonstante#Ein Experiment zur Ermittlung einer Näherung der Gaskonstante, or how the constant was measured to this accuracy. --Ayacop (talk) 09:26, 11 October 2008 (UTC)

If you can translate from the german, the English Wikipedia articles could probably benefit from your help. --Jayron32.talk.contribs 12:46, 11 October 2008 (UTC)

Back to the gas constant. The SI system was carefully constructed to in general, avoid these sort of proportionality constants. Many calculations would require them, except that the units are defined to be compatable in ways that generate proprotionality constants of "1". The situation with "R" is because the SI unit for temperature, kelvin, is created not to be compatable with other SI units, but be compatable with the Celsius scale. Since the size of a Celsius unit is arbitary (there's nothing inherently useful about being 1/100th the difference between the sea-level freezing and boiling points of water), the size of the kelvin is arbitrary as well. One could define a temperature scale where 1 degree was equal to the the amount of energy contained by 1 mole of molecules, and under THAT scale, R would be equal to 1. However, for other reasons of convenience and history, we use the Kelvin scale, so we are stuck with a non-unitary R values. --Jayron32.talk.contribs 13:00, 11 October 2008 (UTC)

I'm not entirely sure I'd agree with that. While interconversion among SI units is very straightforward and generally avoids weird proportionality constants, such constants are almost always necessary in calculations which describe physical processes in the real world. (The energy of a photon is equal to its frequency multiplied by 6.626x10^-34: the Planck constant; the gravitational attraction between two bodies is the product of their masses divided by the square of their separation distance, multipied by 6.674x10^-11: the gravitational constant. And so forth.)

The seven base SI units trace their roots to essentially arbitrary roots which don't have any universal scientific or physical significance. (The meter was originally based on a rough measure of the Earth's circumference; the second on arbitrary divisions in the length of Earth's day; the kilgram tied to the density of water.)

To get rid of arbitrary constants of proportionality, physicists will resort to systems of so-called natural units which peg most physical constants to be exactly 1. Under (for example) Planck units, the speed of light, the gravitational constant, the reduced Planck's constant, Boltzmann's constant, and the Coulomb force constant are all set to be 1, and other units defined from there. Such systems can make calculations dramatically 'neater' and eliminate the risk of 'losing' a constant in a complicated expression. The downside of such systems is that they generate base units which aren't convenient for 'everyday' usage. (The base unit of temperature in Planck units is about 10³² kelvin, and the base unit of time is about 10^-44 seconds.) TenOfAllTrades(talk) 14:51, 11 October 2008 (UTC)

Use of Oil

Generally what percentage of a barrel of oil is used strictly for fuels such as gasoline and diesel? How much is used for plastics and other products? I had heard that oil used for fuels was low - around 20% - and the bulk of every oil pumped out of the ground was for other products like plastic. Is this true142.68.216.154 (talk) 02:35, 11 October 2008 (UTC)

You might want to look at this link [9]. Which deals with oils use for energy. Only 20-30% of the energy we use goes to transportation but almost all of that energy comes from oil. I know that doesn't answer you question but it is probably the origin of you mangled statistic. What comes out of a barrel of oil depends on what the oil is like (where it was found) and how you crack it but this link gives you and idea of how an average barrel gets fractioned [10]. The key chunks of plastics are mostly derived from natural gas. The other components are derived from side products in process of refining oil for gasoline/diesel. Transportation fuel is the largest and most powerful market for oil, plastic just removes 4.7% of the barrel of what would other wise be a waste stream to burn for heat/electcity or maybe converted into hydrogen. In addition consumers can afford to pay more for natural gas to heat their homes and produce electricity than chemical producers can afford to pay for natural gas as a feed stock. The price of natural gas in North America has forced many chemical producers to close up shop and move to places with cheaper natural gas like the Middle East and Africa. I think BASF cited this when they closed plants around 2005 among other companies. I hope that helps.--OMCV (talk) 03:28, 11 October 2008 (UTC)

yeah, the demand for gasoline/fuel oil basically requires economically to "crack" as much of the petroleum that can possibly be used into the proper weights. In addition, the advent of fuel injection and the associated in-tank fuel pumps have made it possible to add the lighter petroleum fractions into gasoline which would have created a lot of vapor lock in the carbureted engines with the fuel pump on the engine, and used to be disposed of. In fact, (according to what i read) the vapor pressure on gasoline has risen enough even just in a decade or two to saturate the vapor capture systems on cars from the 80s. basically, any oil that goes into plastics is leftovers that would otherwise be waste. Gzuckier (talk) 05:22, 11 October 2008 (UTC)

Plants with edible stems

Are there plants other than Rhubarb with edible stems?74.50.200.72 (talk) 06:41, 11 October 2008 (UTC)

Cattails Ζρς ι'β' ^¡hábleme! 07:18, 11 October 2008 (UTC)

Leeks and spring onions are commonly eaten in the UK. Axl ¤ [Talk] 07:20, 11 October 2008 (UTC)

The pedia does it again -- try Edible plant stems for a nice list of munchies. (It doesn't mention mushroom stems/stalks which are not notable but edible.) Julia Rossi (talk) 07:25, 11 October 2008 (UTC)

Mushrooms are also not plants. —Ilmari Karonen (talk) 07:33, 11 October 2008 (UTC)

(ec) A lot of herbs are edible in the whole (or at least their above-ground parts are), so I guess they count. At the other end of the scale, pine phloem is edible (if not very nutritious), though the whole trunk isn't. —Ilmari Karonen (talk) 07:31, 11 October 2008 (UTC)

Rhubarb's culinary cousin Celery certainly qualifies, doesn't it?--Jayron32.talk.contribs 12:44, 11 October 2008 (UTC)

Noisy faucet

My kitchen faucet, which works well otherwise, makes a high pitched whine when running hot water through it. Why? Dismas|^(talk) 15:19, 11 October 2008 (UTC)

There is some air in the pipes. As the air flows through the the narrow opening, it makes a sound. Axl ¤ [Talk] 18:50, 11 October 2008 (UTC)

As water flows through your faucet, there may be regions of turbulent flow; there may also be areas of lower pressure created by the flowing water. (See Bernoulli's principle for more details on how that might arise.)

Turbulence and low pressure can generate noise in at least a couple of ways that would be more dramatic with hot water than cold. First, the solubility of air (mostly oxygen and nitrogen) drops with increasing temperatures. In other words, cold water that left the treatment plant or well saturated with air will be supersaturated after being heated in your water heater. The reduction in pressure and increase in turbulence as the water approaches your faucet will encourage that air to come out of solution and form bubbles; turbulent movement of bubbles generates noise.

Even in the absence of dissolved air, you might still see effects due to cavitation. Hot water has a higher vapor pressure than cold, and hot water may actually boil in regions of low pressure within the plumbing. The formation and subsequent collapse of bubbles of water vapor can generate noise as well. TenOfAllTrades(talk) 19:06, 11 October 2008 (UTC)

Quote identification

With regard to the Fermi paradox: "If there are so many alien civilizations, why haven't they visited us? I decided to do an experiment. I wanted lobsters for dinner. I put a plate on my table, sat down, opened the front door, and waited for a lobster to crawl onto my plate. Three hours later, no lobster came. I ended the experiment, concluding there are no lobsters in the world."

This "quote", which is obviously not word-for-word, is from a show that aired on Discovery Channel a few years ago. --99.237.96.81 (talk) 16:34, 11 October 2008 (UTC)

Lobsters are not a highly intelligent species in an advanced technological civilization with a desire to explore the universe. Axl ¤ [Talk] 18:56, 11 October 2008 (UTC)

If they were, is it a given that we would even notice? ;) --Kurt Shaped Box (talk) 02:01, 12 October 2008 (UTC)

A bad analogy is like a pickle playing chess. TenOfAllTrades(talk) 19:12, 11 October 2008 (UTC)

A quick web search indicates that the story is variously attributed to "a SETI offical", and Timothy Ferris (who is not a SETI official). Ferris is a science popularizer, though, so he may be quoting someone else (or he could be the originator - it's hard to tell). I can't find anything that looks like an "original" source. (Most web hits for "lobster Fermi Paradox" are for Accelerando (book).) -- 128.104.112.147 (talk) 19:42, 11 October 2008 (UTC)

Thanks, but I was actually looking for the name of the show I saw the quote on. --99.237.96.81 (talk) 22:42, 12 October 2008 (UTC)

Well, the other issue is that we may be the only advanced civilization in our galaxy, but our galaxy is such an isignificant fraction of the whole universe its hard to say definately we are the only ones. Back to the lobster analogy, imagine putting out your plate and waiting for a lobster to crawl on it from the moon. There universe may be teeming with advanced civilization, but we lack the ability to detect evidence of it because its too far away. --Jayron32.talk.contribs 20:17, 11 October 2008 (UTC)

The Fermi paradox is really a pretty shakey proposition. We are a civilisation - have we visited any alien species? Could we even if we knew which star system thay lived at? Even if they lived on Proxima Centauri (the closest star to the Sun) - we currently have no clue whatever how we could get to them. Why would we expect that other civilisations would have any better ideas than we do?

Even if they are smarter than we are - or have simply been around a lot longer...if travel between the stars is impossible for us right now - maybe it's impossible, period. Worse still - how do they know we're here? Our SETI detectors are unable to detect a signal unless it's either beamed on a narrow-beam directly at us - or a broadcast signal that's VASTLY more powerful than the most powerful signal we've ever sent into space. We don't routinely beam narrow-beam signals at stars - so they would need much more powerful radio receivers than we currently have in order to hear us...and again - if we don't know how to do that, why should we assume that the aliens do?

Also, we've only been transmitting radio signal with any strength out into space for less than a hundred years - so only aliens within 100 light years could possibly know we're here - and only those within 50 light years could possibly have gotten here after hearing us...if it took them a while to plan the mission and get it funded and launched - they might have to be much closer to have gotten here yet. There are only 1000 stars within 50 light years - and only 50 or so within 20 light years. It's perfectly possible that none of those 50 stars have planets suitable for life.

From what we know - even if aliens are REALLY common around our galaxy - and even if they have close to light-speed travel and radio receivers that are vastly more sensitive than ours, it would STILL be quite surprising if they were able to get here to visit us. Far from being a paradox, Fermi's claim is just wrong.

SteveBaker (talk) 01:28, 12 October 2008 (UTC)

That's assuming that they'd even be interested in contacting us. What's to say that they wouldn't view us as savage, warlike, power-hungry carnivorous beasts with just enough brainpower to be a potential threat to *their* peace-loving civilization should an encounter occur - and decide to steer well clear? Either that, or they see that we're just lumps of meat restricted to 3-dimensional space with no subspace hivemind capability and think 'bleh - who cares about that?'. ;) --Kurt Shaped Box (talk) 02:14, 12 October 2008 (UTC)

Perhaps they're preparing an application for a hyperspatial express route? Axl ¤ [Talk] 09:49, 12 October 2008 (UTC)

Or they've seen what we do to the lobsters whenever they venture forth from the ocean in an attempt to engage in peaceful communication with us... --Kurt Shaped Box (talk) 19:13, 12 October 2008 (UTC)

We are very young on an astronomical scale, and we are advancing at a significant rate. For the purposes of the Fermi paradox, we are not advanced. We have never left this solar system, but we currently emit very large amounts of radio waves, and have even done so with the intent of contacting aliens. We are currently quite capable of interstellar travel, as can be seen by Project Daedalus. Unless advanced civilizations stop sending stop sending out signals, there would logically be roughly spherical areas around where each one began where all, or at least many, of the stars are emitting suspiciously large amounts of a small band of electromagnetic waves. — DanielLC 16:07, 12 October 2008 (UTC)

I've got to disagree.

Project Daedalus is a joke - it requires Helium-3 as a fuel. Which they propose to mine from Jupiter over a 20 year period using robotic probes...we are SO far from even being able to start making the robots that would autonomously mine the fuel for the darned thing - we're nowhere CLOSE to being able to do that. The craft itself weighs 50,000 tons...getting that into orbit would require 2,000 shuttle launches! And all of that to get a small number of teeny-tiny robotic probes to one of the nearest stars. Worse still - those probes would shoot past the star at 12% of the speed of light - leaving only a very short period for observation and science! It's also true that this is not just a matter of science. There is also the matter of politics. There is no conceivable way of getting a government to fund a massive 20 program to mine fuel for a 50 year program which would take another 6 years to report back results. Worse still - nobody who was alive at the start of the program would be alive at the end. The cost of launching the components into orbit alone would be 160 times the cost of the ISS! With present funding levels, NASA would be doing nothing else for a thousand years! Politicians will never allocate that amount of funding to achieve a goal that not one of their voters will live to see through to completion. All of this for at most a couple of hours of science data captured at such a high speed that detailed photography would be impossible! A thousand years of funding for a probe that might just fail when it gets there? I don't think so.

No - we REALLY don't know how to do interstellar travel...not in any kind of practical manner. If aliens managed to build a Daedalus - it would pass us by so quickly that we'd never notice it passing.

You say that we're pushing out a lot of radio waves - but not on an interstellar scale. Recall that the very best radio telescopes we have would be unable to detect broadcast signals of the strength we're putting out from a distance of the nearest star.

You say that we're young on an astronomical scale - perhaps we are - but perhaps we're already pushing the outer limits of what's possible? Because we can't know that there are vast improvements in space technology out there - it's perfectly possible that we're already close to hitting the limits. You can't claim that it's paradoxical that we haven't seen any alien visitors - it's perfectly reasonable given what we know. More to the point - I could claim that because we haven't seen any aliens (and the math makes it seem like there must be lots of them out there) then it must be that we're close to the limits of the technologically possible.

SteveBaker (talk) 20:56, 12 October 2008 (UTC)

Isn't there a theory doing the rounds that radio waves of the strength we tend to emit will peter out into the background radiation after a couple of light years? I seem to remember reading about that a while back. --Kurt Shaped Box (talk) 19:09, 12 October 2008 (UTC)

A point that nobody else raised is that there are many kinds of civilizations that are much more stable than our own. The society in Nineteen Eighty-four is an example--without overpopulation, environmental damage, or global warming, it's much more likely to survive for millions of years than a civilization that's developing quickly.

I also don't believe an advanced species would prefer to use radio waves that spread out spherically. If I had the choice, I would send energy to only the intended destination, not to the boundary of the star system. Laser, or at least directional antennas, are much more energy efficient than ominidirectional radio transmitters. --99.237.96.81 (talk) 22:42, 12 October 2008 (UTC)

That's true - directional transmission makes a heck of a lot more sense. But we aren't talking about aliens talking to us...we're talking about aliens LISTENING to us and then coming to visit. We aren't transmitting to them on nice tight, efficient beams - mostly because we don't know where they are so we don't know where to point the radio beams. So they have to find us based on omnidirectional spherical waves that drop in energy as the square of the distance - and are therefore almost completely indetectable after a lightyear or so of travel.

It would be a different story if we had a powerful ultra-tight-beam transmitter tuned at the "water hole" and undertook a program of transmitting the prime numbers as a series of pulses that were sent at regular intervals to each of the 1,000 nearest stars. That would hopefully catch the attention of any civilisation within ~50 lightyears - and you could start looking for responses from them about 100 years from now.

SteveBaker (talk) 20:15, 13 October 2008 (UTC)

would you freeze in space with nothing on

if i went into outer space without a suit would i freeze instantly? why? is there no oxygen or something?--Majorcolors1 (talk) 17:59, 11 October 2008 (UTC)

You wouldn't freeze very quickly, if at all. In a vacuum (ie. when there's no air) the only way to lose heat it by radiation, which is very slow. You would suffocate long before you froze. We have an article on it: Human adaptation to space#Unprotected effects. --Tango (talk) 19:00, 11 October 2008 (UTC)

Well, it also depends on how you were exposed to the vacuum. If your space suit just suddenly disappeared and all the gas surrounding your body expanded rapidly, the gas would cool so rapidly that the outer layers of your body would be chilled to below freezing. If on the other hand, there was only a slow leak in your space suit until there was no air left, you probably would not freeze, unless your spacesuit was conductive. --M1ss1ontomars2k4 (talk) 20:59, 11 October 2008 (UTC)

Yeah, the gas would cool, but it would be nowhere near your body after a fraction of a second, so how would if affect you? And your spacesuit being conductive won't make any difference since there is nowhere for the heat to go, it still has to be radiated. --Tango (talk) 22:46, 11 October 2008 (UTC)

Well, it depends on the temperature of your spacesuit, I suppose. If it were colder than you (it wouldn't be unless you were in the shadow of something, right?), then you might have a problem. But I'd assume that spacesuits are very insulating, or they'd be conducting heat to/from you all the time. --M1ss1ontomars2k4 (talk) 23:14, 11 October 2008 (UTC)

Your spacesuit is in contact with you and nothing else, so it's almost certainly the same temperature as you. --Tango (talk) 23:25, 11 October 2008 (UTC)

I think the most horrifying thing is that without external pressure your bodily fluids begin to boil, starting with the water on your tongue. Plasticup ^T/C 03:28, 12 October 2008 (UTC)

Your skin is able to provide enough pressure to prevent most bodily fluids from boiling - but your eyes, the interior of your nose, lungs and mouth would certainly have problems with that. For water to boil at body temperature, the pressure has to be down below 100mm of mercury - that's about one eighth of an atmosphere. That's about the pressure at 40,000' - but people have successfully flown unpressurized aircraft at higher altitudes than that. Supermarine_Spitfire#Speed_and_altitude_records - for example, shows a flight up to 51,000' at which air pressure is down to about 76mm of mercury - where the boiling point of water would have dropped to 32 degC - 90 degF. SteveBaker (talk) 03:51, 12 October 2008 (UTC)

Perhaps in those instances the gradual pressure change allowed the liquids to boil off more subtly, but there is no doubt that suddenly being thrust into a near-zero pressure environment makes your tongue boil. It actually happened to one unfortunate gentleman. Plasticup ^T/C 05:48, 12 October 2008 (UTC)

While the plane may not have been pressurised they would almost certainly have been wearing an oxygen mask so the pressure on their mouth and nose would be much greater, and wearing a full face mask wouldn't surprise me. They would probably also have had a pressure suit to apply pressure to the rest of their body (although that wouldn't be vital, since skin can do the job in a pinch, as you say). --Tango (talk) 11:43, 12 October 2008 (UTC)

You would certainly freeze, Tango, although not before you suffocated. Heat loss by radiation is given by the Stefan-Boltzmann law: $P=\sigma (T^{4}-T_{0}^{4})A$

where

σ is the Stefan-Boltzmann constant, about 5.7e-8 W/m2K4

T is the body temperature, normally about 310 K

$T_{0}$ is the cosmic background temperature, about 3 K

A is the body surface area, about 1.7 m2

(I'm ignoring the emissivity of skin which is, to my surprise, close to unity. [11])

The result is about P = 879 watts, dropping to about 528 watts at freezing point. That is a significant rate of heat loss. Let's see how quickly you would freeze.

Energy to cool a 75 kg body from 310 K to 273 K: 75 kg x (310 K - 273 K) x 4000 J/kg.K = 11.1 MJ

Energy to freeze a 75 kg body at 273 K: 75 kg x 333 kJ/kg = 25.0 MJ

At an average 700 watts rate of cooling, it would take (11.1 MJ + 25.0 MJ) / 700 W = 14 hours to freeze you solid. But I imagine that, if you were losing heat at 879 W, you would start getting frostbite quite soon after exposure.

--Heron (talk) 15:47, 12 October 2008 (UTC)

That 3K figure is for deep space away from any heat source. If you are in Earth orbit and not in the shadow of the Earth you are more likely to burn than freeze (the average daytime temperature on the moon is 107°C according to our article and that's pretty much the same as being in space at the same distance from the sun). Space suits have sophisticated refrigeration units in them. You would get very cold in the shadow of the Earth, though, so in LEO you would be going from over 100 degrees above to over 100 degrees below every hour and a half or so. Of course, you lose conciousness in about 15 seconds from hypoxia, so it doesn't really matter. --Tango (talk) 17:09, 12 October 2008 (UTC)

Damn Interesting has a great article on exposure in space here

In the absence of atmospheric pressure water will spontaneously convert into vapor, which would cause the moisture in a victim's mouth and eyes to quickly boil away. The same effect would cause water in the muscles and soft tissues of the body to evaporate, prompting some parts of the body to swell to twice their usual size after a few moments. This bloating may result in some superficial bruising due to broken capillaries, but it would not be sufficient to break the skin. -- Within seconds the reduced pressure would cause the nitrogen which is dissolved in the blood to form gaseous bubbles, a painful condition known to divers as "the bends." Direct exposure to the sun's ultraviolet radiation would also cause a severe sunburn to any unprotected skin. Heat does not transfer out of the body very rapidly in the absence of a medium such as air or water, so freezing to death is not an immediate risk in outer space despite the extreme cold. -- For about ten full seconds– a long time to be loitering in space without protection– an average human would be rather uncomfortable, but they would still have their wits about them. Depending on the nature of the decompression, this may give a victim sufficient time to take measures to save their own life. But this period of "useful consciousness" would wane as the effects of brain asphyxiation begin to set in. In the absence of air pressure the gas exchange of the lungs works in reverse, dumping oxygen out of the blood and accelerating the oxygen-starved state known as hypoxia. After about ten seconds a victim will experience loss of vision and impaired judgement, and the cooling effect of evaporation will lower the temperature in the victim's mouth and nose to near-freezing. Unconsciousness and convulsions would follow several seconds later, and a blue discoloration of the skin called cyanosis would become evident.

-- MacAddct1984 ^{(talk &#149; contribs)} 16:08, 12 October 2008 (UTC)

I don't believe you'll get the bends - and I don't believe that your blood would boil. You are making the mistake of assuming that the pressure inside your body drops to zero. It doesn't because your skin is able to exert a force to keep your innards under pressure (to some degree at least). So pressure inside your body will remain at some fraction of an atmosphere. As I explained before - for water at body temperature to boil, you need the pressure to be below one eighth of an atmosphere - and I'd certainly expect your skin to be able to do that...at least for short periods...in the longer term, you're dead anyway. The liquid on the surface of your eyes, inside your mouth and near other orifices will boil because they WILL fall to zero pressure - but not your blood.

As for getting the bends - I'm not sure what the threshold for getting the bends is - but remember that your body is pressurised to one atmosphere when you are just 32 feet underwater - you can happily snorkel to that depth and come up quickly without getting the bends - and that's the same pressure differential as going from normal air pressure into a vacuum. Note also that astronauts have their space suits pressurised at only half an atmosphere anyway (to keep them flexible apparently) - so the drop is more like coming up from 16 feet to the surface...which I can do in any decent swimming pool with a diving board. How many people get the bends in a swimming pool?

SteveBaker (talk) 20:11, 12 October 2008 (UTC)

The above sounds kind of like what was posited in one sci-fi book I read once (set in 2017, astronauts thought they were in space, trapped underground, to get out had to get through this place w/no pressure & properly fitting suit caused some nasty bulging/bruising; someone might know what I mean). But, I always thought that the lack of pressure in space was so huge that one would literally "pop" instantly. I'll have to read that article on exposure to space when i have more time. I guess it wouldn't be as instnat as I thought.Somebody or his brother (talk) 17:00, 12 October 2008 (UTC)

The classic scene is the one in 2001 (movie) when Bowman is forced to cross from the 'pod' into the main spacecraft without a helmet. SteveBaker (talk) 20:11, 12 October 2008 (UTC)

There's also that scene in Event Horizon where Baby Bear gets locked outside of the airlock. IIRC, he bled from his eyes and his veins began to bulge. Mind you, the ship went to hell and back, so anything's possible... -- MacAddct1984 ^{(talk &#149; contribs)} 22:54, 12 October 2008 (UTC)

That's more or less what happened in Total Recall too...it didn't seem very convincing. SteveBaker (talk) 23:46, 12 October 2008 (UTC)

Robotics - what is static stability?

I find definition of "static stability" as it relates to missiles and whatnot, but not as it relates to robotics. It sounds like it means just the concept that when a robot is at rest it should be stable, but I don't know for sure so I decided to query the WP community. Smaug 18:01, 11 October 2008 (UTC)

Ack nevermind. Just found the answer: "A statically stable robot can stand still without falling over." So I was right. Smaug 18:02, 11 October 2008 (UTC)

Stability is a slightly more subtle thing. With very great care, you can balance a coin on it's edge - but it's not stable - the slightest knock or jolt and it'll fall over. When you leave the coin lying on it's side - then it's very stable - it takes a HUGE jolt to make it flip over. That's "static stability". A statically stable robot would not only be able to stand still - but it would be able to do that with the power turned off - and it wouldn't fall over if you knocked it hard. SteveBaker (talk) 01:05, 12 October 2008 (UTC)

There is also a strange condition between stable and unstable called astable, where the system is in an unstable state, but if disturbed merely goes to another similarly unstable state. Our article redirects to multivibrator which is certainly an example of a device in an astable condition, but not the most informative one. A ball lying on a flat surface is in astable equilibrium, the slightest force on it will change its state, but only to another one exactly the same. A cone has all three types of stabilty: stable if on its base, unstable if on its apex, and astable if lying on its side. In terms of robotics, walking is a challenge to the designer because it requires astable equilibrium. A walker is continually falling, but never does so as he/she immediately moves to another falling state on the other leg. The mechanical equilibrium article appears only to cover static equilibrium. SpinningSpark 12:01, 12 October 2008 (UTC)

Jobs in the private spaceflight industry

It seems that private-sector spaceflight is really taking off (pun not intended) these days. I'm really excited about what's happening with it lately, and I really want to be a part of it all. I'm preparing to go into college starting next semester and I still haven't made up my mind on what I want to specialize in. My question is, what sort of degrees would be useful to the private spaceflight industry? My goal is to collect skills that would make me indispensable to a company in this field. I'm not particularly good at anything as it is. I have some very basic computer programming skills (I could get better, though) and I'm extremely bad at math (I'm aware that this is a huge drawback for what I seek). Does anyone have any suggestions for the career I should choose and what I should learn about in school? Thanks. 63.245.144.77 (talk) 20:11, 11 October 2008 (UTC)

My goal is to collect skills shows you are very wise, that is exactly what will make you indispensable in any field. I'm literally doing the same thing right now. I'm already "competing" against future neurologists(m.d.) who are still in their undergrad. Just think of the bell curve. You have to compete to be in the top 5, in whatever you genuinely want to excel at. The problem is you don't know who the other top four are. You have to be extremely motivated, and (possibly even more importantly) you have to know where to direct your efforts. Its just that (if you live in U.S.A.) most teachers who are great at teaching math, all conspire to make sure that they aren't your math teacher. Math is a dealbreaker, and you need to be an expert at quantitative reasoning. Specific advice: study rigorously and take the LSAT (its a puzzles test mainly), make yourself better at math (ask questions on the math ref desk anytime--always glad to help aspiring rocket scientists), and become a master of metacognition as that's the only way to change your brain's wiring about motivation. Sentriclecub (talk) 21:05, 11 October 2008 (UTC)

There are certain jobs that exist in any industry - personnel (aka human resources), accounts, etc., which you could go for. Jobs specifically related to space flight would be physics and engineering related, most likely, with some mathematicians as well. All of those involve quite a lot of maths, unfortunately... They will certainly need programmers to do simulations and things, but you would need the maths and physics knowledge in order to know what to program. I think, in short, you can't be a rocket scientist without maths! If you're interested in the space tourism side of the industry, you could try studying hospitality and tourism. While you would be learning about land based hotels rather than space hotels, there would be transferable skills. There will be lots of new legal issues with the new sector opening up, so I'm sure they'll need lots of lawyers - working out what jurisdiction a space hotel or moon base falls under could be quite interesting, as would extraterrestrial real estate. Really, they're going to need people from all disciplines, so just pick something that sounds interesting as a degree and then apply for whatever jobs you're suitable for (a lot of jobs just require a degree and it doesn't matter what it's in). --Tango (talk) 20:52, 11 October 2008 (UTC)

Learn Mandarin and business. If by "private spaceflight" you mean space tourism, it's likely many of the punters will be the Chinese nouveau riche showing off their wealth. If you mean it to include privately launched spacecraft in general (including satellites) then a lot of that business will be Chinese entrepreneurs blanketing the middle kingdom with cheap video messaging services and such. -- Finlay McWalter | Talk 21:21, 11 October 2008 (UTC)

There are really a vast range of skills that are going to be needed when private spaceflight really takes off - I would start with a solid grounding in math and science - probably physics, electronics and computer science would be good places to concentrate your efforts. But if you can learn as much breadth of science as possible - and enjoy doing it - then I think your speciality can be almost any science-related subject and you'll find jobs are available. But that wide knowledge base is critical. No small rocketry company can afford to have an extreme specialist in a very narrow field on their staff - they need generalists. SteveBaker (talk) 00:57, 12 October 2008 (UTC)

Obviously you'll want to master all of the intellectual disciplines enumerated by my venerable RefDesk colleagues, but you shouldn't neglect your physical health. Competition for the jobs of first generation space pilots will be nothing short of astronomical, and you will need to be in peak physical condition to remain in contention. Plasticup ^T/C 05:42, 12 October 2008 (UTC)

You're assuming "job in private space travel" means being a pilot - the vast majority of the jobs will be ground based. I didn't even discuss becoming a pilot because the competition is so great it's barely worth considering - you would need to already be an experienced aeroplane pilot, it's not a job you can get straight out of college. --Tango (talk) 11:46, 12 October 2008 (UTC)

Oh - sure. Forget being a pilot. They won't need many pilots and EVERYONE who ever dreamed of being Buck Rogers is going to be after that job. Supply and demand means that that's going to become an increasingly low-grade job. These space-planes are going to be automated to death and you won't need any more skills than (say) an airline pilot needs to fly one. I'm assuming that the interesting, high-dollar jobs are on the ground. Design, test, construction, launch. SteveBaker (talk) 15:10, 12 October 2008 (UTC)

I'd expect the spaceship pilots themselves to be recruited exclusively from the pool of experienced military test pilots anyway... --Kurt Shaped Box (talk) 19:07, 12 October 2008 (UTC)

I think Virgin Galactic are recruiting experienced commercial pilots, not just military. You need a lot of experience, though. While SteveBaker is right about the automation, that only applies to routine flights - if something goes wrong you need to be able to take manual control and know what to do. While lots of people will want the job, there won't be many people qualified, so the supply is actually very low and I would expect them to be extremely well paid (there will be equally well paid jobs on the ground and probably a few better paid jobs, though). --Tango (talk) 20:20, 12 October 2008 (UTC)

Commercial spaceflight is going to be all about weight. For the early passenger flights, they'll be able to charge a small fortune for each seat - filling one of those seats with a non-paying pilot is a costly thing to do. There is really no practical reason why you couldn't fly the spaceplane from the ground and use automation for the majority of the flight. The "when something goes wrong" argument is really untrue. In modern commercial aviation, pilot-induced errors by far exceed pilot-corrected mechanical faults. (Don't consider situations where the pilot lands the plane with one engine out - that could have been done from the ground - I'm talking about situations where the plane would have crashed had the pilot not been physically aboard the plane to fix something.) We could drop the pilot anytime if it were not for the legal ramifications and the fact that people might be a tad nervous about flying in a plane with no pilot. But in a 500 seat 747, adding a handful of crew makes almost no difference to your revenues and keeping passengers happy is more important. But in a 5 seat space-plane, losing 20% of your revenue is a tough business decision. NASA puts human pilots on board the space shuttle - but those people would need to be there to carry out the mission anyway - so the cost of having them there to fly the shuttle is $0. Remember the Russian Buran space shuttle did it's one and only flight entirely under automation. So whether there will be many space-plane pilots in the future ends up being more a matter of how secure the passengers can be made to feel than any actual NEED for a pilot to be physically present in the cockpit.

SteveBaker (talk) 23:02, 12 October 2008 (UTC)

As someone who works in the airplane business (specifically, avionics) I don't think the situation is quite as clear-cut as that; our avionics are not yet good enough (and, importantly, robust enough) to permit pilotless teleoperation on a large scale. In a few years, maybe. Although I will agree that the decision to have a pilot on the first suborbital ships will be partially a technical one and partially a financial one (the non-paying-passenger argument you made).

Oh no, I have contradicted Steve!! :) — QuantumEleven 14:11, 13 October 2008 (UTC)

And what do you do when the radio antenna falls off during re-entry? Even if the radio control works perfectly, I would imagine (I'm not a pilot) it's far easier to fly a plane when you can feel what it's doing that when you can just see lots of numbers on a computer screen. You get genuine feedback from the controls as opposed to simulated feedback that will be inevitably delayed, you can feel the turbulence as it affects the plane rather than just seeing the results on the screen a split second later. Having an actual pilot is very important. Unfortunately, getting accurate statistics on the matter is rather difficult - the failure rate of unmanned spacecraft is much higher, I believe, than manned (there are certainly far more accidents, although there are far more launches so the ratio may not be so different), but they are much more careful with manned craft so that's to be expected. --Tango (talk) 14:31, 13 October 2008 (UTC)

(unindent) I don't agree with ANY of the things you just said!

• What you do if an antenna falls off is what you do if the tailplane falls off. The trick is to design it so that doesn't happen. This is really very easy with stuff like electronics. You can easily have three or four of everything.
• Flight simulators (which I used to design) have hydraulically actuated haptic feedback devices on the controls that have real "feel" to simulate the effects you'd feel in a real plane. They work very well. It would be entirely trivial to measure the forces on the flight surfaces and provide feedback to a pilot on the ground. However, most modern planes don't provide that feedback anyway. An F16 fighter (for example) has a rock-solid steel bar for a joystick that provides no feedback whatever - it doesn't even move! It operates by measuring the force you apply to it. Several modern airliners have little joysticks like on videogames with no feedback whatever. So this is neither necessary - nor difficult to provide if it were necessary.
• The delay in getting feedback isn't going to be critical for space planes. Things just don't happen that quickly until you are about to touchdown on the runway - and at that point you are so close to the transmitter that the speed-of-light delays are irrelevent. Things that need human-response-time rates but not human intelligence can be handled by computers. Things that don't need that response rate but which do need human intelligence can be done from the ground. The only problematic things are things where human response rates AND human intelligence are required - and if you have a system that's designed that way then you have a disaster just waiting to happen because humans are highly fallible when pushed to perform quickly.
• The US military fly planes (called UAV's - Unmanned Aerial Vehicles) by telepresence and computer control all the time. Their pilots mostly sit in the Pentagon building - flying the planes from halfway around the planet via satellite links. This gives them speed-of-light response rates that are about the same as the worst case for an unmanned spaceplane. The technology is extremely well established and there are WAY more UAV's over the skies of Iraq than there will ever be spaceplanes in orbit at any given time. This is a solved problem. The Soviet Buran space shuttle flew an entire mission including launch and landing under remote control...and that was with soviet era hardware from 20 years ago.
• The failure rate of unmanned spacecraft is high because they can save money by cutting back on the safety systems. They don't have anything like the amount of redundant systems when launching a cheap telecomms satellite as they do on the shuttle (for example). But note that shuttle launches are not exactly reliable - having the pilots on board hasn't helped them at all - I don't think there has been a single case where the crew were able to do something to save the spacecraft that couldn't have been done without them.

SteveBaker (talk) 20:03, 13 October 2008 (UTC)

Organisms living inside crude oil

Just out of curiosity, are there any organisms that live in oil deposits in the ground? Surely there's at least some kind of bacteria that have taken advantage of the energy in the oil. 63.245.144.77 (talk) 20:14, 11 October 2008 (UTC)

Check out entropy, oil has less usable energy than the stuff it started out as. Then again, evolution is more a model to fit past data, and it really doesn't hold any prediction ability. (The evolution sentence was a joke. -sorry) If that dream organism existed, it sure would have a monopoly and would propogate very quickly. I'm guessing that biology doesn't work that deep below ground, its sequestered by too much rock. Any organism fit for glycolysis surely would have a field day down there! All those C-H bonds, maybe cockroaches could live down there? Good question, I am very curious myself and hope someone can explain this better. Sentriclecub (talk) 20:46, 11 October 2008 (UTC)

You are incorrect. Evolution is a testable theory that has significant prediction ability. Organisms that are fit for glycolysis are essentially all organisms (yes, including humans). Oil is not sugar. It doesn't matter how good we are at glycolysis; we will in no way be able to digest oil. Cockroaches can't live down there because there's no oxygen. Evolution theory essentially tells us that if there were a way for life forms to get down there and adapt, they would (organisms will adapt to fill open niches). However, they'd have to pass through the intermediate layers of rock, which do not support any life whatsoever. Obviously things cannot live in an area that supports no life, so it's pretty much impossible for any organisms to end up down there. Entropy is also not related to any of this, because entropy has little to do with how much chemical potential energy something has. The amount of useful work that can be done with a given amount of enthalpy is decreased by the temperature times the change in entropy (see Gibbs free energy). Oil has less usable energy (per unit mass, probably) than the organic matter it started out as due to inefficiencies in converting organic material to oil. --M1ss1ontomars2k4 (talk) 20:57, 11 October 2008 (UTC)

Endoliths have been found 3 km down in rock (ref). It seems the only limit on how deep these guys can go is increasing temperature, so it's possible they go down a lot deeper (this article claims maybe 7 km). -- Finlay McWalter | Talk 21:11, 11 October 2008 (UTC)

And there are places where oil literally oozes from the surface of the earth at sea level. No - the remoteness of oil from bacteria isn't a reason they might not have evolved to use oil as an energy source. SteveBaker (talk) 00:52, 12 October 2008 (UTC)

It's hard to find a niche on Earth that doesn't have some kind of life living in it, so I wouldn't be at all surprised if there is something living in oil deposits underground. I know nothing about it, though. --Tango (talk) 20:54, 11 October 2008 (UTC)

Note there are (a rather small minority of) oil geologists who subscribe to the abiogenic petroleum origin theory, wherein oil deposits are not only inhabited by microorganisms (particularly thermophiles, both bacteria and archaea), but are actually made by them. -- Finlay McWalter | Talk 21:03, 11 October 2008 (UTC)

Read Ananda Mohan Chakrabarty to learn about one scientist who created and patented organisms which eat oil. Not sure about the "in the ground" part. It might be undesirable to release bacteria which consumed all the oil under the ground. Edison (talk) 00:03, 12 October 2008 (UTC)

In order to extract usable energy from oil (which is essentially hydrocarbons), one would need be able to create compounds with lower internal energy (enthalpy, or H) than the hydrocarbons. This is generally accomplished via oxidation. However, in order to oxidize these compounds, a source of some usable oxidizing agent needs be present. The most likely source of this is oxygen itself, and underground oil has no access to this. From a purely chemical point of view, that oil underground is safe from nearly any biological organism that might be able to "eat it". There may be some that exist that can consume oil at the surface, but that is because of the availibility of free oxygen. --Jayron32.talk.contribs 11:48, 12 October 2008 (UTC)

The fact that oil has "bugs" is well known although I can't find a good that talks about it in specifics. There is more chemistry that life than preform than photosynthesis and standard respiration, take a look at extremophiles. Even without oxygen life goes on. One of methods that eventually get used on every oil field is water injection (oil production). Its a standard part of enhanced oil recovery. According to Matthew Simmons book this process has been in effect for sometime within the Ghawar Field. But that is important for other reasons. Our concern here is that if oil producers flood wells with water containing dissolved oxygen life flourishes in the oil field eventually complicating or preventing oil recovery. It standard practice to use aquifers of sterile brine from strata above the oil fields for the purposes of water injection. This brine is for all intensive purposes free of oxygen and life. In leu of a brine aquifers, water form the surface needs to have the oxygen removed and life killed prior to injection. Regardless check out the water injection (oil production) I think its the only place on wikipedia that covers life in oil. As far as the science goes I don't know how much is well known publically besides methods to kill the "bugs" described in Society of Petroleum Engineers publications. Oil companies would rather people not know that they are exterminating rare forms of life in the process of bringing them their gasoline.--OMCV (talk) 03:39, 13 October 2008 (UTC)

Part of what inspired me to write this question was the memory of a ninth grade biology experiment we did on the first day of school where we put some water and some vegetable oil in an empty water bottle and then shook it up creating little shperical globs of oil, which are essentially the same structures in cellular membranes. Anyway, I explained this experiment to a friend of mine who wasn't in that class and I just said "oil" not being specific, so he made his own version...with motor oil. Nevertheless, it still worked the same even though it wasn't transparent. Anyway, a few weeks later, I noticed long strings of bacteria or mold or something growing in my experiment, which I stupidly set in a window sill in my room (source of energy). Coincidentally, My friend had set his in a window too and...lo and behold, there were strings of bacteria in the motor oil too. I know from personal experience that life can survive in oil if there's a source of energy, but can it survive under the ground? I'd be extremely surprised it it couldn't, actually. I recently found out that there's huge slimy colonies of bacteria in the cracks between rocks in gold mines in South Africa three miles below the surface. Scientists think that cells living at such extreme depths were the cells that repopulated the surface after huge meteorite impacts destroyed all surface life billions of years ago. So bacteria can definitely get that deep. If bacteria can live off of rocks using chemosynthesis as a source of energy, they can live off of oil in a similar way.

I guess I just answered my own question, but I'm still curious as to the nature of things living in oil. I'm surprised I can't find any info on it on google.63.245.144.77 (talk) 05:29, 14 October 2008 (UTC)

Strange thermodynamics question

Say we have some ideal gas. It undergoes an adiabatic expansion from 1 Liter to 2 Liters and does no work. What are ΔU and ΔH for this process? I already know ΔU (ΔU = ΔQ + ΔW, all of which are zero), but I don't quite get ΔH. So far, we have that dH = dU + PdV + VdP. dU is zero, PdV is zero (no work done). But what's VdP? Since no work is done, can we say that the external pressure is zero and constant, and thus VdP is zero? --M1ss1ontomars2k4 (talk) 20:30, 11 October 2008 (UTC)

Your question is self-contradictory, I'm afraid. If you let the ideal (or any) gas expand adiabatically from V₁ = 1 L to V₂ = 2 L, it will perform work equal to integral of PdV from V₁ to V₂. On the other hand, if you put external pressure to zero, the gas will not do any work, but the expansion will not be adiabatic. The only way to stay adiabatic AND to have zero pressure is to have initial pressure = 0. That implies either an ideal gas at initial T=0, or ideal gas with zero particles in the volume considered. Hope this helps. --Dr Dima (talk) 03:58, 12 October 2008 (UTC)

Why would it not be adiabatic, if external pressure were zero? Reversible adiabatic processes are isentropic but this is not really reversible, if the external pressure were zero. --M1ss1ontomars2k4 (talk) 04:04, 12 October 2008 (UTC)

Sorry, I misunderstood your question. I thought you are referring to reversible (isentropic) adiabatic expansion process. If you are referring to non-isentropic adiabatic expansion with zero work performed, the enthalpy H should stay constant. indeed, H = U + PV. In your process (non-isentropic adiabatic expansion with zero work performed) U does not change, and PV is zero all the time so it cannot change (both PdV and VdP are zero). Thus, ΔH = 0. For an ideal gas that means that you stay on an isotherm. Indeed, U = DNT/2 where D is number of degrees of freedom per particle, N is total number of particles, and T is temperature. As long as U stays constant, so does T. Hope this answers your question. For clarity, it is important to realize that the initial state for your process is out of the equilibrium: pressure is zero but NT/V is not zero. That happens when you suddenly remove a wall separating gas in volume V₁ from the void in the rest of the volume V₂, where V₂ > V₁. And a final note: many physicists, including myself, normally use the words "adiabatic process" only when they are talking about reversible adiabatic ( = isentropic ) process. A process in which ΔQ = 0 and ΔN = 0 but entropy increases is simply referred to as "irreversible process". Keep that in mind and you'll be fine ;) --Dr Dima (talk) 01:17, 13 October 2008 (UTC)

Intelligent Life in the Universe/Voyager Golden Record

I have been interested in the Golden Record that is on Voyager 1 and 2. I learned about how it is there in case Voyager encounters intelligent extraterrestrial life on its journey. If other intelligent extraterrestrial life created something similar and it went through our solar system, would we have any way of knowing? —Preceding unsigned comment added by 75.169.21.144 (talk) 21:28, 11 October 2008 (UTC)

It would probably be difficult to spot unless it passed very close to Earth. I expect any radio transmissions would be pointed back towards where it's come from, if there even are any (the Voyager craft will stop transmitting millennia before they reach other stars). Because they operate so far from the sun, they use nuclear power rather than solar panels, which means they don't have a particularly large reflective area so would be very bright. You would probably only see one if it passed close to Earth and you happened to point a large telescope in the right direction at the right time. --Tango (talk) 22:39, 11 October 2008 (UTC)

if such a device entered the solar system, it might have a circuit to trigger a beacon which would send radio sugnals to get our attention. When Voyager was launched, we did not know how to build a device which would "wake up" and send out signals after tens of thousands of years. Edison (talk) 23:56, 11 October 2008 (UTC)

It's probably safe to say that we still don't know how to build such a device. We have no idea what happens to our spacecraft after tens of thousands of years, since we've only had most of the supporting technology and advanced materials for less than a century. We could design a system to be "very reliable" and develop some system (software?) to wake it up in a few millenia, but there is no way we could test the reliability of it over thousands of years. HALT testing only goes so far in estimating certain types of failure. Nimur (talk) 00:37, 12 October 2008 (UTC)

Most of it doesn't need to be operational for 10,000 years, it just needs to sit there, so there isn't a whole lot that can go wrong (you would want some good shielding from radiation, etc, but that's about it). I think the real problem isn't the time, it's the cold, electronics break pretty quickly if they get too cold and the power requirements of keeping the probe warm for 10,000 years are most likely beyond us at the moment. --Tango (talk) 11:51, 12 October 2008 (UTC)

The point is that once Voyager gets away from the Oort cloud, there is no reason why it shouldn't keep moving off into the galaxy for millions or even billions of years. Over all that time - it is perhaps possible that some alien species would find it. It seems unlikely that they'd be able to decypher it though. The plaque and record are really poorly designed IMHO. SteveBaker (talk) 03:30, 12 October 2008 (UTC)

I think the likelihood of anything finding it is probably less than the likelihood of making any sense of it. Assuming something beyond dumb and impossible luck, any species that had the technology to locate that particular need in the interstellar haystack should be able to figure out the technology without too much difficulty, I'd imagine. --98.217.8.46 (talk) 03:33, 12 October 2008 (UTC)

That doesn't diminish how undeniably cool it is. We recorded the fundamentals of our species in a (hopefully) universal format and sent it careening into the depths of space. That has an intrinsic value to our species, even if it never facilitates communication with another. Plasticup ^T/C 05:23, 12 October 2008 (UTC)

I agree that it's an interesting statement, one that says more about the act of creating it than it does about its potential discovery. But it's worth noting that the selection of content says more about the people who created it than it does about the human species. Not all members of our species would agree on what the fundamentals were. For example, from what I can tell via Voyager Golden Record, there were no religious texts included whatsoever. No doubt Sagan may have thought that "Johnnie B. Goode" was more fundamental to understanding US culture than the Bible, but I'm sure there would be those who would vehemently disagree. ;-) --98.217.8.46 (talk) 13:33, 12 October 2008 (UTC)

It's about putting our best foot forward, I suppose. Plasticup ^T/C 16:14, 12 October 2008 (UTC)

There don't seem to have been any texts included at all, religious or otherwise. It looks like among the vocal music there was none with a religious text, but it's not as though an extraterrestrial could tell what the words meant anyway. -- BenRG (talk) 19:15, 12 October 2008 (UTC)

Well if we were really a space-faring society, i.e. one with personal and commercial inter-planetary travel, then I suspect that Space Traffic Control would monitor every rock much bigger than a ping-pong ball and fairly quickly notice a new metallic object entering the solar system. Obviously that makes assumptions about what the distant future of space travel might be like, but there is no reason to assume that ET will be as primitive as us. Dragons flight (talk) 06:03, 12 October 2008 (UTC)

If Voyager I ever travels through a planetary system similar to our solar system then it will be moving very fast indeed by the time it reaches the vicinity of an Earth-like planet's orbit. At the moment it is about 100 AU from the Sun and is travelling at about 17 km/s. If it fell into the gravity well of a star similar in mass to the Sun then at 1 AU from that star it would be travelling 10 times as fast, so 170 km/s. At this speed it covers a distance equal to the diameter of the Earth's orbit in about 20 days. So not much time to detect it, and quite difficult to catch it if it is detected. Gandalf61 (talk) 10:31, 12 October 2008 (UTC)

Ummm, your numbers are off. Falling into the sun's gravity well would only give you ~42 km/s at Earth's orbit. Dragons flight (talk) 16:51, 12 October 2008 (UTC)

42 km/s is escape velocity from the solar system starting from the Earth's orbit. But Voyager I is going much faster than escape velocity, mainly due to gravity assists from Jupiter and Saturn on its way out of the solar system. In the absence of interactions with planets, velocity of a free-falling spacecraft is inversely proportional to the square root of distance from the Sun (by conservation of energy), so 17 km/s at a distance of 100 AU becomes 170 km/s at a distance of 1 AU. Gandalf61 (talk) 20:19, 12 October 2008 (UTC)

I don't follow your calculation. Falling adds to the velocity, it doesn't multiply it by something (what it adds is dependant on initial velocity, but I can't see how you end up that result). --Tango (talk) 20:38, 12 October 2008 (UTC)

No, 17 km/s approximately goes to ${\sqrt {17^{2}+42^{2}}}\approx 45$. The energies, which are proportional to velocity squared, will add not multiply. You seem to just multiplying by 10 since that is the sqrt of 100, which is wildly wrong. Dragons flight (talk) 21:15, 12 October 2008 (UTC)

Yes, you are right. Escape velocity is inversely proportional to the square root of distance from the Sun, not velocity of spacecraft. Total cock-up on my part. Gandalf61 (talk) 10:11, 13 October 2008 (UTC)

What does Radioactive Waste look like?

I read the article on radioactive waste, but I'm still not sure what the final "stuff" looks like. In popular culture, it's usually depicted as this glowing green stuff, but I have a feeling that's not really what it looks like. I guess in other words, what does the radioactive waste inside of those containers look like? ScienceApe (talk) 22:37, 11 October 2008 (UTC)

Radioactive waste can be unprocessed, in which case it's just raw fuel rods (containing fuel pellets). So that's just thin shiny cylinders filled with little metal cylinders the size of short stacks of coins. For reprocessed waste, high-level waste can be encapsulated in a number of ways; one is in glass blocks (or disks). -- Finlay McWalter | Talk 22:48, 11 October 2008 (UTC)

Radioactive waste (low level) can be clothing, rags, mops, cardboard, bottles, and many other materials which could become contaminated with radioactive materisl, as when there is a fluid leak in a power plant which releases radioactive materials that must be cleaned up. It goes in drums and gets stored. Edison (talk) 23:54, 11 October 2008 (UTC)

What's the fluid usually? ScienceApe (talk) 01:13, 12 October 2008 (UTC)

My understanding is that most high-level radioactive waste is produced in reprocessing plants—acids and washes used to separate out plutonium from other fission products and things like that. Probably just looks like sludge. If you google "hanford waste tanks" you can find images of a lot of liquid waste—nothing very interesting. Certainly not glowing green goo. --98.217.8.46 (talk) 03:16, 12 October 2008 (UTC)

So it would look like just some thick brown fluid? ScienceApe (talk) 14:42, 12 October 2008 (UTC)

For the record, the Cerenkov radiation in nuclear reactors causes them to glow blue, not green. Radioactive waste stored in water could also glow blue if there was enough of it, but more likely it would be broken up into small enough portions that there would not be a human perceptible glow. Dragons flight (talk) 04:13, 12 October 2008 (UTC)

Another form of nuclear waste is the power plant after decommissioning. Especially the material that contained the reactor core. So that would look like construction material, I suppose. Metal plates and such? Amrad (talk) 07:01, 13 October 2008 (UTC)

And concrete.

Note that when it comes to disposal, sludge is not favoured, because if the container were damaged it could leak into groundwater. I believe, the British Nuclear Decommissioning Authority favours "microencapsulation", where liquid wastes are immobilised inside containers with a grout. AlmostReadytoFly (talk) 10:06, 13 October 2008 (UTC)

October 12

Image licensing

HI,I AM DOING THIS PROJECT ABOUT NORTH AND SOUTH POLE AND I JUST WANT TO ASK YOU THAT IF I CAN PRINT SOME PICUTER THANKYOU VERY MUCH FROM MEENAKSHI —Preceding unsigned comment added by 68.183.31.96 (talk) 00:18, 12 October 2008 (UTC)

Yes

SpinningSpark 11:23, 12 October 2008 (UTC)

Smallprint for lawyers to read

Almost every photo on Wikipedia is freely licensed. This means that you may re-use or modify the photos (including printed copies). For any specific image, check its license information, which will provide details on what the image owner requires regarding re-use. Also see Wikipedia:Image copyright tags for general information. In general, if you are using these photos for a school project, that would be permissible under most of the image licenses on Wikipedia. Nimur (talk) 00:32, 12 October 2008 (UTC)

I have no idea what cutting pie has to do with the North and South poles....--el Aprel (^facta-_facienda) 00:36, 12 October 2008 (UTC)

Hi! It's OK to print most pictures that are on Wikipedia - but there are a few exceptions. All of the photos at our South pole, Antarctica, North pole and Arctic are OK to copy. You can also go to our sister site "WikiCommons" - and type "North pole" or "South pole" into the search box...you'll find also that there are "categories" of photos: Category:South_Pole and Category:North_Pole. There is also a bunch of photos of the Amundsen-Scott south pole station. All of those photos are OK to print.

If you need to know about other pictures on Wikipedia, what you need to do is to click on the photo you are interested in and when the image's own page pops up, it should look a bit like this one: HERE. Now you need to scroll down and look where it says either: "Licensing" or "Permission (Reusing this image)" - if it says something about "Fair use" then it's not OK.

SteveBaker (talk) 00:47, 12 October 2008 (UTC)

Though honestly if you are using it in an elementary school assignment I don't think anybody cares about the copyright status. --98.217.8.46 (talk) 03:29, 12 October 2008 (UTC)

You mean ANY school project? Who's going to sue you because you used, say, Coca-Cola's logo in a school assignment? That would just make the copyright owner look bad. --M1ss1ontomars2k4 (talk) 04:06, 12 October 2008 (UTC)

Well, I left out "any" because I could imagine some school projects in some scenarios where stuff like that could matter. (A dissertation is a "school project", in a sense, and you have to be mindful of copyrights with those.) But yeah. Really not worth worrying about for run-of-the-mill assignments. Falls under fair use pretty solidly. --98.217.8.46 (talk) 13:25, 12 October 2008 (UTC)

It is important to teach a respect for the copyright law. If kids get the idea that they can copy anything anytime - they are going to get into a lot of trouble in later life. Copyright laws are annoying and a big pain in the butt - but they are laws - and it's important that kids realise that. The idea that copyright holders don't "care" about little things like school projects is likely true - but that's not true of trademark law - where if you don't actively pursue infringements you can lose your ownership of them. Hence, CocaCola may well be forced to pursue even "irrelevant" infringement at the level of a high school project. SteveBaker (talk) 14:58, 12 October 2008 (UTC)

Oh yeah, sorry, I was forgetting about all those CocaCola billboards at the North Pole and the pictures of them in Wikipedia to catch out the unwary. Context! please. SpinningSpark 18:24, 12 October 2008 (UTC)

Large corporations will most certainly sue schools over misues of their trademarks: Disney has done it to day care centers and most other companies will as well. They will also always win, and it isn't only because they have lots of high powered lawyers. Under intellectual property law, there is a concept known as "trademark dilution"; once a trademark (be it a word, logo, or character, basically any symbol of your company) has entered the common lexicon, you can no longer use it as a trademark. Basically, if Disney did NOT aggressively defend its trademark, and was shown to allow, say, a day care center in Florida to use Mickey Mouse in their logos without proper permission, then it would set a precedent for anyone to use it. Disney cannot be selective in allowing infringements of its trademarks; it either has to expressly require that all uses are licenced, or it has to allow all uses by anyone for any purpose. As a result, large corporations can and do pursue these cases... --Jayron32.talk.contribs 18:35, 12 October 2008 (UTC)

Jayron is exactly right. Consider for example a school student project which then becomes entered in the state science fair and wins, subsequent to which prominent newspapers publicize the event c/w pictures. The way copyright law works is that you have to pursue any violations that come to your attention, otherwise you fall foul of the equitable doctrine of laches and your trademark becomes public domain. Aspirin and kleenex are examples of former trademarks that became common names. Companies don't want to pursue daycares, they have to. Franamax (talk) 04:56, 14 October 2008 (UTC)

What colour would you say best describes the upper mandible of a male Eclectus?

Question as topic. A user has suggested that 'candy-corn-coloured' (as stated in the article at present) is less than ideal. I'm inclined to agree.

Any suggestions? I'm thinking 'saffron' - though I'll readily admit that colour naming is not my strong point... --Kurt Shaped Box (talk) 02:52, 12 October 2008 (UTC)

It looks like scarlet (or orange) with a bright yellow tip, though I see what the phrase "candy-corn-coloured" means when I look at the photograph of the parrot. Just "candy corn", without the "coloured", might work for those who have seen candy corn (and for those who haven't, click here [12]) but candy corn has a white tip. ៛ Bielle (talk) 03:09, 12 October 2008 (UTC)

I agree. When writing for Wikipedia, one should strive to keep specific cultural references like "candy-corn" out of articles like that. We are read in dozens of countries around the world - most of whom will never have seen or heard of candy-corn. Most people in the USA know what it is - and what color it typically is - but I doubt whether people from other countries would know. Sure, you can provide a link to the article candy corn - but it would be much better to use a proper description of the color rather than to send people off on hunts for obscure references like that. Better still - just put a nice color picture in there. SteveBaker (talk) 03:26, 12 October 2008 (UTC)

People who don't know candy corn? My God, man! I don't believe it. I won't believe it! Plasticup ^T/C 05:15, 12 October 2008 (UTC)

Well, I've never heard of it. But I wouldn't want to interfere with your deeply held beliefs. Algebraist 09:08, 12 October 2008 (UTC)

Looks orange-yellow to me. [By the way, I have no idea what "candy-corn" is. ;-) ] Axl ¤ [Talk] 11:04, 12 October 2008 (UTC)

Candy corn is little multi-colored globs of sugar, usually served at Halloween in the U.S. I've never had a taste for it... --Jayron32.talk.contribs 13:00, 12 October 2008 (UTC)

Nobody has tasted it. None have been produced since 1934. The entire supply at that time has simply been recycled each year. -- kainaw™ 17:08, 12 October 2008 (UTC)

Yeah, every year the entire supply is melted down to make Circus peanuts. Interestingly, every year the entire suply of Circus peanuts is melted down to make candy corns, resulting in a never ending cycle of recycling inedible "candy". --Jayron32.talk.contribs 18:01, 12 October 2008 (UTC)

I think you've all forgotten that the sole purpose of candy corn is to insert two of them - pointy-end-down - between teeth and upper lip for the purpose of scaring little sisters into thinking you have turned into a vampire on all-hallows evening. Subsequent consumption of these objects can only be accidental. SteveBaker (talk) 19:46, 12 October 2008 (UTC)

I wonder if Eclecti will eat candy corn, if offered? --Kurt Shaped Box (talk) 22:41, 13 October 2008 (UTC)

For what little it's worth, I rather like the stuff. —Tamfang (talk) 01:31, 14 October 2008 (UTC)

I'd never seen, nor heard of 'candy corn' until yesterday. When I saw the term used in the article, I was imagining something like toffee popcorn - or maybe candyfloss. --Kurt Shaped Box (talk) 19:28, 12 October 2008 (UTC)

...which is PRECISELY why we shouldn't use it. SteveBaker (talk) 19:48, 12 October 2008 (UTC)

Be better to pick from shades of yellow and link to the chosen shade. Bazza (talk) 14:21, 13 October 2008 (UTC)

Copper(II) Sulfate Crystal

Hello. Are there any catalysts or fancy methods to make a solution of CuSO₄ • 5H₂O and water crystallize faster, clearer, and with clean cuts? Thanks in advance. --Mayfare (talk) 04:08, 12 October 2008 (UTC)

The problem is that speed and quality are exactly competing factors in crystalization. Any method used to make crystals quickly (such as rapidly dropping solution temperature, or "scratching", or adding seed crystals) will cause LOTS of small, imperfect crystals to form. If you want faster, then create a hot supersaturated solution of CuSO₄, and let it cool to below the precipitation temperature. Drop a small "seed crystal" of CuSO₄ • 5H₂O into the mixture, and viola, you'll get crystals, but they will likely be small and imperfect. If you want high quality crystals, you should aim for making them AS SLOW as possible. You should start with the same hot, supersaturated solution (this is generally made by boiling a saturated solution of CuSO₄ until the volume reduces, but there are ABSOLUTELY NO crystals in the solution) and then place it in some insulation, and let it cool VERY SLOWLY. After several days, crystals should form, and they should be nice and big and well defined. --Jayron32.talk.contribs 11:38, 12 October 2008 (UTC)

1876 Supplement to Harper's Bazar, No.13 and No. 25

I recently discovered two tapestry patterns from 1876 each are double sided on one side clothing patterns on the other side maybe embordry prints/designs. The patterns and instructions are printed on old newspaper and folded in half twice. The paper is very fragile to handle or measure without causing damage. I want to know more about these documents and how to share them? —Preceding unsigned comment added by Yma99 (talk • contribs) 09:35, 12 October 2008 (UTC)

I copied this question from the new users page as how to handle old newspapers is bit beyond a question on how to use Wikipedia. SpinningSpark 09:47, 12 October 2008 (UTC)

Perhaps call a museum in your nearest large city? Or go to the local library and ask? Either of these will have people who can direct you to specialist advice. You might check though whether these are already scanned in a web archive somewhere. Franamax (talk) 04:42, 14 October 2008 (UTC)

photographic chemicals

Up to the 1940's photographers knew various chemical formula for making black & white negatives and prints. Where can I find this chemistry? —Preceding unsigned comment added by 122.111.64.194 (talk) 09:58, 12 October 2008 (UTC)

A good place to start looking is History of photography and follow the links there. Timeline of photography technology may also link to useful articles. SpinningSpark 11:06, 12 October 2008 (UTC)

Which formula do you want? I have books listing many. Edison (talk) 23:21, 12 October 2008 (UTC)

electron configuration of Barium

Hi is the following electron configuration for I have come up with for the element barium correct?

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2. Thanks. —Preceding unsigned comment added by 139.222.240.110 (talk) 12:43, 12 October 2008 (UTC)

Looks right to me. Barium is in period 6, group IIA, which should have the configuration "...6s2" and it doesn't look like you missed any core orbitals either. --Jayron32.talk.contribs 12:57, 12 October 2008 (UTC)

Yeah, that's right. Source: Clicky —Cyclonenim (talk · contribs · email) 13:58, 12 October 2008 (UTC)

thanks :) —Preceding unsigned comment added by 139.222.240.66 (talk) 17:50, 12 October 2008 (UTC)

Using nuclear weapons as a propulsion system for spacecrafts

I'm reading Neal Stephenson's new book Anathem and in it he describes a rather unusual propulsion system for spacetravel (this isn't a big spoiler at all, feel free to read on even if you haven't read the book yet).

The idea is this: a spaceship would have one side on it that is covered by a so-called "pusher plate", which acts as a big shield, capable of withstanding a nuclear blast. A nuclear weapon is deployed on the other side of it and detonated, and thus the spaceship would fly off with enourmous velocity (essentially rocket jumping, but with nuke instead of a rocket and a spaceship instead of a player).

I've thought a little bit about this, and it seems to me that this wouldn't work. The reason a nuclear weapon will blow everything around it to smithereens (like that famous exploding house that we've all seen), is that it has an enourmous shockwave. But space is essentially a vacuum, there's no medium for a shockwave to propagate through. So it wouldn't impart basically any momentum to anything near it. The only thing that would happen (I imagine) is that it releases lots and lots of energy through electromagnetic radiation, which would barbeque any organic material nearby, but it wouldn't actually have a shockwave. I don't know if electromagnetic radiation departs any momentum on the things it hits, but even if it does, it's not all that much, is it?

Look at the sun: the sun is basically a mindnumbingly big nuclear reaction, much much bigger than any nuclear weapon, yet it doesn't "propel" it's satellites to enourmous speeds. The earth isn't flying off into space because of the sun. So why would this system work? 195.58.125.56 (talk) 17:51, 12 October 2008 (UTC)

See Project Orion (nuclear propulsion). Its "performance" section explains how they intended to design special bombs such that they'd maximise the kinetic yield of the nuclear explosive, which they'd then impart to the spacecraft itself by collision. -- Finlay McWalter | Talk 17:56, 12 October 2008 (UTC)

(e/c) Neal stephenson is just one in a long line of science fiction authors who have used the idea proposed by Stanislaw Ulam in or about the late 1950s. See Nuclear pulse propulsion.--Fuhghettaboutit (talk) 17:58, 12 October 2008 (UTC)

Yep - project Orion is famous in Sci.Fi. circles - lots of books have used it. I'd argue that the rather subtle manouvering that's implied would be impossible for such a craft - you've only got an all-or-nothing thrust mechanism. You can't do a "three second orbital injection burn" with a motor that either kicks you up the backside with 20 megatons or does nothing at all. But with such a large craft - you'd need something pretty powerful. SteveBaker (talk) 19:39, 12 October 2008 (UTC)

If I were building such a craft I would include a conventional rocket engine as well for the subtle stuff. Just use the nukes for simple acceleration. You need to be able to get a safe distance from anything you don't want to blow up/irradiate anyway, which requires some kind of propulsion. --Tango (talk) 20:40, 12 October 2008 (UTC)

If you don't mind wasting a bit of ΔV, you can dial down the thrust by delaying the explosions by various amounts, to detonate the bombs further from your ship. --Stephan Schulz (talk) 22:45, 12 October 2008 (UTC)

Nah, you only use nukes for intersteller travel. For manuvering you use conventional muntions. "Three grenades to starboard. Aye, Captain!".  ;-) Dragons flight (talk) 22:49, 12 October 2008 (UTC)

At least that will improve chances for peaceful first contact with the Minbari. --Stephan Schulz (talk) 22:52, 12 October 2008 (UTC)

Just to address the main question in it: it's not the shockwave that pushes the ship. You put in some plastic (basically) and the heat/radiation of the bomb turns it into a very dense plasma which expands/explodes and that pushes things. Basically. --98.217.8.46 (talk) 02:14, 13 October 2008 (UTC)

Also interesting is Nuclear salt-water rocket. Essentially a continuously exploding nuclear pulse propulsion rocket. ScienceApe (talk) 00:13, 13 October 2008 (UTC)

Wow! That's a cool idea. I like it! SteveBaker (talk) 01:37, 13 October 2008 (UTC)

What good an anal probe?

I've just thinking about all those personal accounts of (supposed) abduction and experimentation upon humans by aliens. How much useful data would one actually be able to collect on a human subject by probing its anus? Can anyone think of what it is that the prober might actually be trying to discover about the probee by doing this?

The taking of skin, blood, sperm and tooth samples at least kinda makes sense from a 'research into the species' viewpoint. --Kurt Shaped Box (talk) 19:24, 12 October 2008 (UTC)

It's a particularly unpleasant and degrading experience which elicits sympathy from those the abductee tells about it. --Tango (talk) 19:35, 12 October 2008 (UTC)

Apparently aliens are fascinated by cows (e.g. cattle mutilation). Perhaps they are looking for evidence of beef consumption? Dragons flight (talk) 19:50, 12 October 2008 (UTC)

Temperature and eating habits come to mind. —Cyclonenim (talk · contribs · email) 20:53, 12 October 2008 (UTC)

As does inspiring the fear of invasion. Julia Rossi (talk) 21:44, 12 October 2008 (UTC)

I think they are looking for our brains - they must be in an out-of-the-way place as we only occassionaly use them. SpinningSpark 22:20, 12 October 2008 (UTC)

If this were truly happening - an alien wanting to do a "non-invasive" investigation would of course start off by checking and sampling material from every obvious external orifice. SteveBaker (talk) 22:28, 12 October 2008 (UTC)

Though can cross the galaxy but somehow they haven't invented x-rays, cat scans, or MRIs? Dragons flight (talk) 22:44, 12 October 2008 (UTC)

Sampling...extracting fluids and solids. SteveBaker (talk) 23:50, 12 October 2008 (UTC)

They have. But they have a huge co-pay. - Nunh-huh 22:57, 12 October 2008 (UTC)

You know, I would consider someone sticking something up my rear end to quite invasive... --Tango (talk) 23:01, 12 October 2008 (UTC)

Fair point, Steve - but I don't recall reading many (any?) accounts of oral probing in the abduction accounts. --Kurt Shaped Box (talk) 23:33, 12 October 2008 (UTC)

Observer bias. The people who were asked nicely to say "Ahhhh" and got a lollipop at the end of the probing didn't complain as much as the ones who suffered less dignified forms of testing.  :-) SteveBaker (talk) 23:50, 12 October 2008 (UTC)

I forget the poet and the poem, but it was on the lines of "Aliens came from another planet/and studied humans/and decided they were a means/for the production/of shit". Any outside observer studying our hygiene habits, and the attention paid by humans to the emanations of dogs (picking up in bags and carrying it around fer gawdz sake), would surely conclude that there must be something very important up there and feel the need to investigate. Franamax (talk) 04:35, 14 October 2008 (UTC)

how much gas?

How much gas would an average human be able to pass in his or her lifetime? ("Would" because normally we don't try to maximize this. I mean if they were to eat a lot of beans all their life -- nothing chemical/artifical). —Preceding unsigned comment added by 82.120.232.170 (talk) 21:41, 12 October 2008 (UTC)

Well, the Mythbusters measured between 3 and 10 'gas passing incidents' per day on a normal diet - with a typical volume of around 13ml per 'incident'. Let's pick 5 per day as an average. Over a 70 year lifespan - that's 70x365x5x13ml = 1600 liters - which you could visualize as being about the volume of a good-sized house. On a 'bean-intensive diet, the Mythbusters registered 22 incidents per day - with a peak volume of 170ml in one hour - so we should say that about five times the 'normal' amount is probably about the maximum. But there are HUGE error bars on those numbers. I'd believe 5 times more or 5 times less than that 1600l number. SteveBaker (talk) 22:46, 12 October 2008 (UTC)

1 cubic meter is exactly 1000 liters, so 1600 liters is 1.6 cubic meters. That's about the volume of a 1.2 m x 1.2 m x 1.2 cube. --99.237.96.81 (talk) 22:56, 12 October 2008 (UTC)

Er - yeah. Sorry - I slipped a zero or three there! Wow...that's *NOTHING*. SteveBaker (talk) 23:52, 12 October 2008 (UTC)

Steve, we're allowed to screw up like that - you're not! ;) hydnjo talk 00:59, 13 October 2008 (UTC)

According to Britannica, a lactase deficient person will produce (or rather, the persons gut bacteria will produce) 500ml to 1000ml of gas from one glass of milk. So if you really wanted to go for it and do record breaking stuff, ten glasses per day would not be too challenging and would yield (for Steve's 70 years) 70x365x10x750ml = 191,625 litres. Which is a bit more house sized. SpinningSpark 23:39, 12 October 2008 (UTC)

October 13

Is our solar system flat ?

In all models and illustrations of our solar system that I have seen, the planets appear to be traveling in one plane. This seems strange to me. Don't the planets actually revolve in different orbital planes, and if so, is there some way that the distance between planets varies with time, maybe to the point of possible collision between two planets? —Preceding unsigned comment added by 58.167.231.238 (talk) 00:11, 13 October 2008 (UTC)

Solar system says: Most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic. The planets are very close to the ecliptic while comets and Kuiper belt objects are usually at significantly greater angles to it., so yes, they're all basically on the same plane. This came about because the planets all formed from a spinning disk of stuff. As for the second question, no the planets are too far away from each other to ever collide. --Sean 00:18, 13 October 2008 (UTC)

Actually, if you ignore the now disgraced Pluto, they do all revolve in roughly the same orbital plane. Our articles on the solar system are actually some of the best at Wikipedia, most are featured or good articles. See Solar system and Planet for some broad overviews. As far as planetary inclination, which is the term for deviation from the mean orbital plane of the solar system, the largest is Mercury at 7^o off center. All other planets are less than 3.5^o off center. Now, lots of other objects do orbit at distinctly greater angles outside of the orbital plane, but none of the main planets do. See List of spherical astronomical bodies in the Solar System for a full list of planets and their stats. The planets are all in fairly stable orbits, and stand no real chance of coliding with one another (even Pluto and Neptune, which swap place in terms of distance from the Sun, do not actually physically cross orbits, and would never collide). Objects in the Solar System do colide all the time, but this usually occurs because some of the smaller objectes, with more eccentric orbits, will collide with a planet. There is no chance for two planet-sized objects to collide. --Jayron32.talk.contribs 00:25, 13 October 2008 (UTC)

Pluto IS a planet, dammit. 67.184.14.87 (talk) 20:30, 13 October 2008 (UTC)

The distances between planets varies dramatically because they all orbit the sun at different rates. Mars (for example) goes around the Sun once every 1.9 earth-years. So if Earth and Mars were as close together as they ever can be - then about a year later, they'll be on opposite sides of the Sun...and about as far apart as they can ever get. But I presume that you are asking whether the radius of the orbits changes. Well, things are a bit more complicated. The planetary orbits are not circles - but ellipses - so the distance of the each planet from the sun varies slightly through the planetary-year. Those ellipses are also slowly rotating - so each planet's path through the solar system looks a bit like a flowery spyrograph pattern. While this pattern seems very stable and is unlikely to change much in the future, the solar system is an "n-body problem" - which is an unsolved mathematical problem - and is believed to exhibit chaotic properties. That means that we can't reliably predict what will happen over the very long term - and it's possible that some strange combination of conditions could perturb the stability of the solar system. While the planets seem to know where they're going - that's not true of moons. It is known (for example) that our Moon is gradually spiralling away from the Earth and will eventually disappear off into space - it's unclear what the consequences will be when that happens. One of Mars' moons is going to break up in the next million years and form an amazing ring system around that planet. Pluto's orbit is thought to be somewhat unstable. So things are not as stable and clear-cut as they seem. SteveBaker (talk) 01:33, 13 October 2008 (UTC)

The moon is backing away from the Earth because it is increasing its orbital angular momentum by stealing from the Earth's rotational angular momentum via tidal drag. Given a long enough time the Earth rotation would slow to match the orbital period of the Moon, and the system would be doubly tidally locked (like Pluto and Charon are). Once that happens the Moon will no longer recede from the Earth. The mechanisms responsible for its recession don't allow the Moon to escape. A back of the envelope calculation suggests that the orbit of the moon can grow to about 5 times it's present size before the Earth's angular momentum is entirely depleted, so that sets an upper limit on the ultimate size of the orbit. Dragons flight (talk) 07:24, 13 October 2008 (UTC)

Actually, if it expanded to 5 times its current distance I think it would outside the Earth's Hill sphere (our article says the Earth's Hill sphere is about 1.5 million km and the Moon's orbital radius 0.384 million km, and 5*0.384=1.92>1.5), so it would be perturbed by the Sun and would eventually enter a direct solar orbit. --Tango (talk) 11:11, 13 October 2008 (UTC)

squid blood

I was watching a tv show about colossal squid. The narrator said that the squid's blood was blue. I have read through the articals on squid, giant squid and colossal squid but can't find any information as to why the blood is blue. Why is this? Also, are there any other animals that do not have red blood?

Thanks. —Preceding unsigned comment added by 216.154.17.55 (talk) 03:30, 13 October 2008 (UTC)

It's bluish. All your questions are answered in hemolymph and hemocyanin articles. --Dr Dima (talk) 03:46, 13 October 2008 (UTC)

short answer: it uses copper instead of iron to grab the oxygen. rust is red, but copper oxide is green. see articles mentioned above for details.Gzuckier (talk) 00:23, 14 October 2008 (UTC)

to know mechanism

please give me satisfactory mechanism of how blood cells come out from the bone marrow? which mechanism do they follow to come out?

i also want to know that through which respiration method RBC respire?

please send me answers of all this questions. i am a biology teacher.

thanking you. —Preceding unsigned comment added by 117.196.0.122 (talk) 04:59, 13 October 2008 (UTC)

For the record, you sound like a biology student. I'd suggest consulting your teachers manual and colleagues for answers. If you can't find them there, read Red blood cell and Bone marrow. In reponse to your second question in particular, consider the following: What enzymes or cellular machinery does a cell require to perform aerobic or anaerobic metabolism? What do RBCs have/lack? --Shaggorama (talk) 07:28, 13 October 2008 (UTC)

Orthogonal translation

Wikipedia doesn't have an article for this. What is it? --M1ss1ontomars2k4 (talk) 05:50, 13 October 2008 (UTC)

Some context would be useful here. Is this phrase just the "plain-English" sum of its parts, i.e., approximately "Orthogonal translation--motion at a right angle to some other direction"? DMacks (talk) 05:57, 13 October 2008 (UTC)

I agree, context is needed to answer this question properly, but orthogonal transformation might be meant if this is a mathematical concept, and the Maths desk might be able to help more]] SpinningSpark 07:08, 13 October 2008 (UTC)

quantum mechanics

de broglie predicts that matter is a wave, and hence has a wavelength, right? when my teachers explained this, they usually used a baseball or something to show that the effects were small for large objects. well, let's say that plancks constant was large, like 1 J*second. would the baseball have a discernable wavelength? well, the equations of quantum mechanics say that λ=h/p, and so, since the baseball has momentum, it would have a wavelength. but the baseball is just a myriad of electrons, protons, and neutrons. so wouldn't it be those particles which have the large wavelength, rather than the baseball. this question can also be generalized to other concepts like the uncertainty principle: are analogies with macroscopic objects valid? —Preceding unsigned comment added by 65.92.231.82 (talk) 09:32, 13 October 2008 (UTC)

Both the baseball and each constituent would have a wavelength. An experiment has been done with a very small balls, in fact with buckyballs of 60 atoms (see Quantum Mechanics in that article), and the complete balls produce a diffracton pattern just like electrons. Dmcq (talk) 10:04, 13 October 2008 (UTC)

The de Broglie wavelength of any object is given by the simple equation:

$\lambda ={\frac {h}{p}}$

where h is Planck's constant and p is the object's momentum. Since momentum is directly proportional to mass, then the wavelength is inversely proportional to mass; i.e. the more massive an object is, the shorter the wavelength. For any significantly large object, the wavelength of its DeBroglie wave will be so small as to be meaningless, like wavelengths smaller than the diameter of a proton. --Jayron32.talk.contribs 18:13, 13 October 2008 (UTC)

Clockwise or Anti-Clockwise

I know our solar system travels around the our galaxy the milky way. But I do not know if it travels clockwise around the core of the galaxy or Anti-clockwise. By that I mean if the direction pointed by the north pole of the Earth is defined as up, are we traveling around the core, in a clockwise manner or anti-clockwise manner? 122.107.229.49 (talk) 09:40, 13 October 2008 (UTC)

For that matter, I don't even know if the Earth travels clockwise or anti-clockwise around our Sun. —Preceding unsigned comment added by 122.107.229.49 (talk) 09:42, 13 October 2008 (UTC)

Using the Right-hand rule with north in the direction of the thumb, the earth rotates counterclockwise as can be seen from the sun rising in the east. We go around the sun anticlockwise as well, but that axis is tilted by 23 degrees relative to the north pole. (Warning: Tilting causes seasons)

According to [13] the sun rotates around the galactic centre with an axis that's tilted 117 degrees relative to the earth's north. So we're basically going clockwise around the galaxy. According to the sun article, that's at 220 km/s so it takes the sun 8 days to move a distance equal to the distance between us and the sun. Adding the speed of the milky way with respect to the rest of the universe, we're going at a comfortable 370 km/s.

Sundial shadow

The milky way you can see in the sky are simply stars along the galactic plane, which gives you a bearing on where we are. You can see the 117 degree tilting in that the milky way is never aligned exactly east-west in the sky. (If it had been tilted 90 degrees, it would have run north-south and east-west if by 0 degrees) EverGreg (talk) 10:37, 13 October 2008 (UTC)

As an aside, the shadow on a sundial travels "clockwise" (in the northern hemisphere). Clock hands just copy the motion of the shadow. Saintrain (talk) 16:50, 13 October 2008 (UTC)

FISH

In fluorescent in situ hybridisation, how many fluorescent entities must converge on a point to make it visible? How small a point is it likely to be for a typical probe and its unique recognition sequence?

I don't have an answer to your question, but we do have a page on the technique: Fluorescent in situ hybridization (U.S. English spelling) --Scray (talk) 11:01, 13 October 2008 (UTC)

I've created a redirect. --Tango (talk) 11:14, 13 October 2008 (UTC)

I consulted the article before coming here. It was not helpful in this case. :( ----Seans Potato Business 15:25, 13 October 2008 (UTC)

I can't speak to what is typical for the FISH technique, but there is no reason why with the right probe and a sufficiently sensitive sensor that the answer couldn't be one. In general it helps both for visibility and background rejection to have a brighter signal, so FISH may be designed to operate with a greater abundance, but from a technical perspective detecting an isolated fluorescent tag is certainly possible. Dragons flight (talk) 16:52, 13 October 2008 (UTC)

Yup, all you need is one. In FISH, a filter is used on the microscope to exclude all light that isn't within the range emitted by the flourescent tag, so it is an extremely sensitive technique. It is often used to locate individual binding sites on a chromosome, which are tiny! Poke around google for some images. --Shaggorama (talk) 18:13, 13 October 2008 (UTC)

The article is actually a pretty good description of how FISH works. Since the technique is based on hybridization of a unique probe sequence to the target chromosome, only one "fluorescent entity" can be present at a single point on the chromosome. Usually this is a large (50-300 kb) piece of DNA (a bacterial artificial chromosome or fosmid which can be propagated in bacterial culture and purified in large quantities) that is labeled with fluorescent nucleotides so that multiple fluorophores are incorporated into the probe. The size of the probe largely determines the sequence specificity (i.e. whether the probe binds to only one position in the genome), and the sensitivity (brightness) of the fluorescent signal. There will almost always be some background non-specific hybridization that comes from repeated sequences within the probe or low complexity sequences in the genome that are just "sticky", which requires optimization for each given probe. The spatial resolution will depend highly on the conformation of the chromosomes you are using -- the highly condensed mitotic chromosomes will give much lower spatial resolution than interphase ones or the stretched out "fiber FISH" technique (which can supposedly give a resolution of around 1 kb). From a theoretical perspective, one might be able to identify a 16-20 base pair sequence that is present only 1x in the genome of interest, label an oligonucleotide probe and use some fancy tricks to amplify a fluorescent signal so that it could be detected by a highly sensitive microscope. The smallest reported probe is around 50 bp (see this), but from a practical standpoint it isn't done this way very much. —Preceding unsigned comment added by Medical geneticist (talk • contribs) 20:35, 13 October 2008 (UTC)

Questions about massive sqid

1. Is there a theoretical maximum possible size for squid?

2. Would it be possible to capture a giant/colossal squid alive to place on display in an aquarium? —Preceding unsigned comment added by 84.71.115.30 (talk) 12:10, 13 October 2008 (UTC)

Tthere are some theories on how large an animal can get. A predator for instance, may be limited by the size of its prey [14]. But according to Deep-sea gigantism, there may be advantages to being big in the deep ocean. But noone has calculated an exact maximum size. In [15] it is speculated that an unusually large squid had messed-up hormones so in any case there'd always be giant freaks that didn't fit into the theories. As for the second question, it's probably easier to catch a young one and raise it to adulthood in captivity. EverGreg (talk) 12:33, 13 October 2008 (UTC)

Squid belonging to the 'large' species decompress and die if you haul them up from the deep to the surface, don't they? --Kurt Shaped Box (talk) 22:36, 13 October 2008 (UTC)

composite aircraft

Good Day,I would like to know how many composite (carbonfiber/fiberglass) Federal Aviation Administration certified aircraft were built every year from 1998 to the present.Please if possible list by manufacturer. I would also like to know if any projections are made by the manufacturers or the F.A.A. for the future of composite aircraft.65.15.124.92 (talk) 18:44, 13 October 2008 (UTC)

O-ring and G-ring

I'm confused by the term O-ring; it seems to have one or two additional meanings beside the one found here, referring to metal rings. Is there a 2nd meaning to the term "O-ring" that means the kind of double-looped steel ring that is commonly used as a keyring? I found this meaning e.g. here. My theory is that people don't know how this type of ring is properly called and make an analogy to the related G-ring - "it's like a G-ring but in the shape of an O". Is that right, or is "O-ring" a proper name for this thing? The 3rd possible meaning of the term "O-ring" can be found in items of jewellery such as necklaces and earrings. If my interpretation of the pictures I found via Google is correct, here the term means something like "a bigger decorative circular ring sideways attached" - is that right?--84.155.219.241 (talk) 19:22, 13 October 2008 (UTC)

I have always only heard O-ring to mean a big rubber gasket or washer of some sort. Though it certainly may have other uses. --Jayron32.talk.contribs 19:27, 13 October 2008 (UTC)

Sorry, I need to rephrase the 2nd part of my question. I'm also wondering whether there is a 2nd meaning to the term G-ring, found in items of jewellery such as necklaces and earrings. If my interpretation of the pictures I found via Google is correct, here the term means something like "a bigger decorative circular ring sideways attached" - is that right? 84.155.219.241 (talk) 19:30, 13 October 2008 (UTC)

How does NASA calculate trajectories?

When NASA calculates the trajectory of an interplanetary space probe, do they use Newton's formula's (classical physics) or Einstein's (relativity)? 67.184.14.87 (talk) 23:07, 13 October 2008 (UTC)

Newton is plenty good enough for trajectories. The systems that provide the thrust and measure the position/velocity aren't accurate enough to show the consequences of relativity at the speeds that current spacecraft move. SteveBaker (talk) 23:53, 13 October 2008 (UTC)

What is the theoretical wavelength upper limit for electro-magnetic waves?

Extremely low frequency waves have a wavelength of ~ 10,000km - 100,000km. Is there an upper limit? The size of the Universe?, or as the Universe is unbounded is the upper limit infinite? Jooler (talk) 23:04, 13 October 2008 (UTC)

What triggers a missile to explode?

What, exactly, is it that causes a missile, specifically a surface-to-air missile, to explode? Does it have guidance built in so that when it reaches a specific point in space, it goes "I have now reached my target; I shall explode now", or does it have sensors to detect that, or a mechanical trigger which goes off on impact? (Could you theoretically grab a missile (gently) out of the air and hold it without setting it off?) What happens if the conditions for exploding are not met and the missile gets lost or starts running out of fuel to keep seeking the target? Does it explode, or become inert/safe? SamSim (talk) 23:11, 13 October 2008 (UTC)

We'd tell you but then, well you know...  ;) hydnjo talk 23:30, 13 October 2008 (UTC)

Well, that scuppers my plans for stealing SAM's and asking on Wikipedia how to set them off. I guess I won't post my question on how to launch them either. Anyone know a good place to sell unused surface-to-air missiles? eBay? Franamax (talk) 04:08, 14 October 2008 (UTC)

Its called a # Fuse_(explosives), If missile goes wrong and is heading back to you, there is a thing called a Break up system that, well, breaks up the missile without detonating the warhead.

--GreenSpigot (talk) 01:04, 14 October 2008 (UTC)

Clearly one could build a missile to explode due to the passage of time, due to altitude, due to impact, or due to proximity to a possible target, as well as due to triggering by the party who launched it. Edison (talk) 05:17, 14 October 2008 (UTC)

Why can pulse be normally abnormal?

I'm a little confused, after reading the article on the pulse as it relates to the body. I understand it's not always the same as heart rate - so is that it? Because, I'd been under the assumption one would just check for 10 seconds or so and multiply by 6, or at least 15 and multiply by 4. Does this mean that pulse rate can have a few little skips, and if so, why? Is it slight movements - the hand moving a bit while trying to measure at the wrist? is it the different things that cause the waves in the heart's normal sinus rhythm? Or, what? —Preceding unsigned comment added by 209.244.187.155 (talk) 23:44, 13 October 2008 (UTC)

Pulse rate and heart rate are identical under most circumstances (the exceptions mainly occurring when the heart is pumping abnormally). But neither is as regular as, say, a CPU. It's not a clock. It speeds up, it slows down, based on a variety of variables: exertion, rest, drugs, stress, emotion, vagal nerve stimulation, etc. So 10 seconds is too short a time for a reliable estimate of heart rate. Count for 30 seconds and multiply by 2, or for a full 60 seconds. And you should expect the pulse to fall within the normal range (60-100) rather than to be the same each time you take it. - Nunh-huh 23:57, 13 October 2008 (UTC)

Perhaps the OP is asking about regularly irregular pulse, e.g. second degree AV block. These rhythms are irregular, but beat patterns can be grouped in a way that can be described as regularly irregular. In particular, for these rhythms one should count for a few cycles of the beat group, or about a minute, before estimating the heart rate. --Scray (talk) 02:34, 14 October 2008 (UTC)

October 14

Plutos' core

Is Pluto's core generally hot or cold? From this image, it said the center is made of alloy, iron-nickel, and the mantle is rock and ice. I thouhgt Pluto's core would not be hotter than the surface of Venus, but may still be warm enough for water to become a steam? Since Pluto's atmosp is only 1/1000 of Earth's fraction, the globe colour would be gray perhaps yellow-tan or orange-yellow tinge add to the gray.--Freeway19 00:50, 14 October 2008 (UTC)

Do we have answer to is Pluto's center hot or cold. Some scientist beieve it is made of ieon nickel with alloys stuff. Will It put pluto's center to at least 100 C. I know it is unlikely to be 500 C or 1000 C. --Freeway19 02:30, 14 October 2008 (UTC)

Probably over 1000 C. Hundreds of kilometers of rock and ice is a very good insulator; it holds in heat. If there is a liquid ocean, people think it starts only ~250 km down. [16] Dragons flight (talk) 03:54, 14 October 2008 (UTC)

Light Concentration

What exactly is a Light Concentration diagram? I have failed to find one on Google, or anywhere for that matter. And if someone can answer that, could you tell me where I could find one for Lake Baikal (in Russia), or what one would look like?72.65.101.51 (talk) 00:53, 14 October 2008 (UTC)

Could you mean light intensity? A diagram or graph would show the intensity dropping with depth. Graeme Bartlett (talk) 03:07, 14 October 2008 (UTC)

Some mathematical physics expression

$\displaystyle {D_{x}^{I}\rho _{I}V_{I}T_{I}\ {\overline {B_{xy}^{(I\,II)}}}}$
This is an expression I saw in a picture written on a blackboard behind Niels Bohr. Could someone please tell me what it pertains to and means and what articles would have more information about whatever it is? Thanks in advance, Ζρς ι'β' ^¡hábleme! 02:14, 14 October 2008 (UTC)

I don't think you are going to get a definite answer from just that. It might help to know how old Bohr was in the photos since physics evolved a lot in his lifetime. Off hand, I'd guess some form of quantum mechanics expression, with ρ a density, V a volume, T a temperature, D_x a differential operator in x, and the I and II denoting two kinds of material. If you assume he's dropping constants (as theorists often do) then it looks like a derivative operator in x acting on an energy times some interaction function B. What B is, I haven't a clue. Often "B" denotes a magnetic field, but you'd be unlikely to sub and superscript it that way if that were the case.

Also, I could be totally wrong. Dragons flight (talk) 04:53, 14 October 2008 (UTC)

Is Heisenburg's Uncertainty Principle really universal?

Perhaps it's just personal, but I find this Principle to be a fraud. Surely, though, I'm not right and everyone else is wrong. It states that by locating a particle you make its momentum uncertain and vice versa. But a Principle of physics should accurately describe matter and the universe, not our ineptitude as observers. For example, if we were omnipotent gods, and could 'see' these particles, Heisenburg's Principle surely would not make sense. If really small aliens possessing intelligence and observational powers were the same size of these particles, surely THEY could determine the position AND momentum for any given unit of time.

I find it like cave men trying to understand tigers, only the tiger eats them when they come near him. They only way they can study him is to throw spears at him until he's dead. Would these perhaps thoughtful cavemen have a Tiger's Uncertainty Principle, and state "Well a living Tiger is just UNKNOWABLE" because they lack the proper tools to analyze the Tiger?

I feel that Heisenburg's Uncertainty should not be presented as a Principle, a 'rule,' or really any part of Physics other than a statement along the lines of "We suck as observers and can only 'detect' these particles by shooting high energy particles AT it, thereby ruining our original setup."

Why is this not presented in this way, or has noone made these objections? Am I missing something?

Ehryk (talk) 05:41, 14 October 2008 (UTC)Ehryk